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Indole Test: Principle, Procedure, Purpose, and Results
Continue ReadingWhat is Indole Test?
Indole test is one of the biochemical tests which is conducted on the bacterial species to detect the ability of pathogen to produce indole from tryptophan in the presence of a group of enzymes known as tryptophanase.
Generally, it is a qualitative test, which is performed as part of the IMViC test and is used to differentiate the members of the Enterobacteriaceae family.
It is very important in identifying the different species of bacteria like Escherichia coli, proteus, Morganella, etc.
This plays a central role in characterizing the coliforms and it is denoted by various differences of the indole test and also in combination with other biochemical tests.
It is used as a traditional method to distinguish Indole negative Enterobacter and Indole Positive E. coli and Klebsiella.
Variation of the test is known by Ehrlchs reagent that is used when the test has been performed in non-fermenters and anaerobes.
Indole Test Purpose
Indole test is used to detect the ability of the organism to produce enzyme tryptophanase.
Indole Test Principle
As mentioned before, Indole test is one of the biochemical tests which differentiates the coliform from other members of the Enterobacteriaceae; by detecting the ability of the pathogen to produce enzyme known as tryptophanase.
Tryptophanase hydrolyses the amino acid known as tryptophan into indole, ammonia and pyruvic acid.
It is usually known as intracellular enzyme or endoenzyme. Pyruvic acid thus produced can be used by the organism in the Krebs’s cycle or it enters into the glycolysis pathways and it is used to synthesize other necessary compounds for the cell.
The culture medium used for indole test involves Sulphide, Indole, motility (SIM) or nutrient peptone, either of the given media provides necessary amino acid a tryptophan which acts as a substrate the reaction.
Thus, the organism is able to produce indole as a main product and ammonia as a byproduct.
Kovac’s reagent is used as the reagent for this test which reacts as a side product in catabolizing the tryptophan and this results the indole to form a Rosindole dye which is cherry red in color.
Hence the formation of cherry red color denotes the positive indole test and it is not in the sense that E. coli is positive to indole and Klebsiella is negative to it.
Indole Test Materials
• Filter paper
• Watch glass
• Test tubes
• incubator
• Peptone broth-enriched with amino acids and tryptophan
• Bacterial samples of Escherichia coli and Klebsiella species
• Kovac’s reagent.
Indole Test Procedure
Indole test can be performed in two ways such Rapid Spot test and tube test.
1. Rapid Spot Indole Test
To perform rapid spot test, a piece of filter paper is taken and is it moistened using the reagent.
An isolated colony from a cultured medium is taken using an inoculated loop and it is rubbed against the moistened filtered paper.
Then the filter paper is observed for color change
Rapid Spot Indole Test Interpretation
If the appearance of blue color is observed in the filter paper within 20 minutes, then it indicates the positive result of indole test.
If there is absence of any colors in the filter paper then it denotes the negative result for indole test.
2. Tube Indole Test
Either peptone broth or medium is prepared using Sulphide, Indole and motility in the test tubes and the test tubes are autoclaved at 15lbs/inch pressure for about 15 minutes.
By using the sterile wire, broth is inoculated with the samples that were provided and the test tubes are labelled with the specific name of the organism.
Further the test tubes are incubated at 37ºC for 24 to 48 hours.
After the proper incubation, test tubes are taken from the incubator and are added with four to eight drops of Kovac’s reagent in each of the test tubes, in such a way that reagent touches the walls of the test tubes.
After adding the reagents, the test tubes are placed in between the palms and they are shaken to mix the reagent such that it mixes well with the culture.
The test tube is left undisturbed till the solution stands and development of cherry red color is observed at the surface of the media.
Tube Indole Test Interpretation
Indole test is diagnosed as positive if it appears in the cherry red color; it also indicates the presence of E. coli.
Indole test shows negative result, if there is no formation of red color, and indicates the presence of Klebsiella.
Uses of Indole Test
• Indole test is generally used to test the ability of an organism to utilize tryptophan and to produce indole.
• This test is used to differentiate the members of the Enterobacteriaceae family as a part of IMViC test.
• This test also helps in differentiating the Proteus mirabilis from other species of Proteus.
• This test also differentiates the indole positive E. coli and the Indole negative Enterobacter and klebsiella.
• Along with this, this test also helps in differentiating K. pneumoniae, which is indole positive from K. oxyotoca, an indole positive and also in differentiating Citrobacter freundii, an indole Negative from the Citrobacter koseri, an indole positive species.
Indole Test Citations
- Indole-spot test in bacteriology. Tech Bull Regist Med Technol . 1963 Mar;33:47-50.
- Product in indole detection by Ehrlich’s reagent. Anal Biochem . 2015 Sep 1;484:21-3.
- Technique of indole test. Acta Pathol Microbiol Scand . 1959;46:349-60.
- Spot indole test: evaluation of four reagents. J Clin Microbiol . 1982 Apr;15(4):589-92.
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Urease Test: Definition, Principle, and Procedure
Continue ReadingWhat is Urease Test?
Urease test is one of the biochemical tests which helps in detecting the fermentation of alkaline in the urine which results in the production of ammonia by the microorganisms.
The alkaline fermentation results in the formation of urea. Usually, the fermentation process of urea happens in the presence of an enzyme “Urease”, which results in the formation of two molecules of ammonia and carbon dioxide.
This test was first developed by Christensen in the year 1946 to differentiate a pathogen enteric bacilli.
Christensen used Urea Agar base initially to test the urease, so it was later named after him as Christensen Urea Agar.
Urease activity is considered as an important characteristic for identifying the species Proteus.
Urease activity helps to identify the proteus from the non-lasting fermentation members of the Enterobacteriaceae.
During Urease test, the organisms tend to utilize urea as the source of nitrogen which helps in producing enough amount of ammonia to overcome the buffering capacity of the culture medium. When the color of the medium changes due to pH, it conveys the test result.
Objective of Urease Test
To test the ability of an organism to synthesize the enzyme urease, which hydrolysis the enzyme urease into urea.
This test also enables us to differentiate Urease-positive proteus from other Enterobacteriaceae
Microorganisms Types and Urease Test
Urease test helps in identifying the following microorganisms.
1. Gram negative enteric pathogens including those of Yersinia spp
2. Fastidious Gram-negative rods-Brucells, Pasteurella, Helicobacter pylori.
3. Gram-positive rods-Corynebacterium and Rhodococcus spp.
4. Yeasts-Cryptococcus spp. This test is performed directly as a rapid test to detect the presence of H. pylori in the gastric biopsy samples.
Urease Test Principle
Medium of the urea culture is made up of either broth or agar, which contains urea and phenol red acts as pH indicator. Many of the organism especially which causes urinary tract infections, produces an enzyme urease, and catalyzes the splitting of urea in the presence of water, and releases tow molecules of ammonia and the carbon dioxide the ammonia then combines with the carbondioide and turns the medium into alkaline thud turning the indicator from its natural orange yellow to bright pink color.
This test is performed as performed to identify the several genera and species of the Enterobacteriaceae family including some species like Klebsiella, Proteus, and some Citrobacter and Yersinia and also some of the species of Corynebacterium.
This test also helps in identifying the pathogens such as Cryptococcus, Brucella, Helicobacter pylori and other bacteria’s which produces the enzyme ureases.
Disks are available to combine Urea and the phenylalanine deaminase, which allows one-disk test is used to identify the species proteus, Morganells and Providencia. it also helps in separating them from Klensiella and Yersinia enterocolitica.
The disk reactions are rapid and sensitive and allows the rapid detection of disease-causing agents such as Brucella and cryptococcus.
Reagents, Media and Supplies Required for Urease Test
Both agar slant and broth media are used for detecting urease production. Agar media includes the Urea Agar Base namely Christensen Agar and the broth includes Urea broth. Besides the usage of rapid test kits are available for detecting the activity of urease.
The composition of the urea and agar base is listed below.
Ingredients Gram/liter Dextrose 1.0 Sodium chloride 5.0 Peptic digest of animal tissue 1.5 Monopotassium Phosphate 2.0 Agar 15.00 Phenol red 0.012 Supplies:
Loops or sterile wooden sticks are used. Saline or water in a small plastic tube for the disk test, Incubator at 35ºC and 30ºC.
Urease Test Procedure
1. Preparation of media
Initially 24.52 grams of dehydrated medium is dissolved in the 950ml of distilled water in a beaker.
The solution is heated to bring into boil in order to dissolve it in the medium completely.
Then the prepared suspension is sterilized by autoclaving at 15 lbs. pressure for 121º for 15 minutes.
after sterilizing the beaker is taken out and cooled to 50ºC.
Then 50ml of sterilized 40 percentage of urea solution is added to the beaker and mixed well.
The medium is then dispensed into the test tubes and they are set in a position to obtain an agar slant.
2. Urease Activity
To test the urease activity a loop full of isolated colony is taking with the help of an inoculating loop and it is inoculated further on the agar slant that were kept prepared.
The inoculation is done on just the slant it must be checked often that it should not be stabbed.
Then the tubes are incubated by loosening their caps at 35 to 37ºC. When using non-fermenters, it is incubated at 30ºC.
Now the tubes are observed for the appearance of pink color for as long as 7 days.
If there is no change or growth is seen on the agar slant, further inoculation using heavy inoculum can be done.
3. Rapid Urease Test
This test is often called as CLO test which is Campylobacter-like Organisms, and it is commonly used for rapid identification of Helicobacter pylori.
For performing this test biopsy is taken from the mucosal layer of the antrum of the stomach and the sample taken is placed in the urea broth and phenol red indicator is added.
The tube is then noted for the change from yellow to pink color.
Interpretation of Urease Test
A positive test result is demonstrated when intense orange color changes into the bright pink color, in approximately 15 minutes to 24 hours.
Where as in negative test result there will be no color change.
Urease Test Citations
- HUITAI rapid urease test: a new ultra-rapid biopsy urease test for the diagnosis of Helicobacter pylori infection. J Dig Dis . 2007 Aug;8(3):139-42.
- Accuracy of the Ultra-Rapid Urease Test for diagnosis of Helicobacter pylori infection. Gastroenterol Hepatol . 2017 Dec;40(10):651-657.
- A time-saving-modified Giemsa stain is a better diagnostic method of Helicobacter pylori infection compared with the rapid urease test. J Clin Lab Anal . 2020 Apr;34(4):e23110.
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Biuret Test For Protein: Definition, Principle, and...
Continue ReadingWhat is Biuret Test?
Biuret is a compound which is produced by heating the urea at a temperature of 180ºC. Biuret test is one of the chemical tests which uses Biuret reagents that contains 1% of copper II sulphate.
Cu2+ which is present in the Biuret agent and forms a complex with the peptide bond in the proteins. Thus, this test helps in determining the peptide bonds in the substance.
When two acids are attached through amino and carbonyl group, they are called as peptide bonds.
The fundamental unit of protein is usually termed as amino acids that are connected through peptide bonds.
Biuret Test Principle
Biuret test is commonly called as Piotrowski’s test, which is named after the physiologist Gustaw Piotrowski, who first documented this test in the year 1857.
Other new methods have been developed based on the principle used in this method such as Modified Lowry test and the BCA tests.
Biuret test works with the certain set of principles and they are listed below. When Biuret reacts with dilute copper sulphate in a presence of alkaline, a purple-colored substance is formed, this color is formed due to the chelate complex or due to the copper co ordination complex.
Cupric ions chelate a violet-colored complex using the oxygen of water and the unshared electron pairs of the peptide nitrogen.
As this complex absorbs light in 540nm, the sample turns into a purple color at the present of protein complexes. And hence it changes color from blue to violet.
However, color intensifies depending on the number of peptide bonds according to the increase in number of protein molecules.
Depending on the above principle, we can detect the amount of peptide bonds that were present in any of the biological fluids.
This reaction occurs in a compound which have at least 2, H2N-CH2-, H2N-C, and H2N-CS groups or other similar groups which are directly attached to the nitrogen or a carbon atom.
Generally, one molecule of cupric ion is attached to the six peptide linkages through the coordinate bonds.
Materials and Reagents Required for Biuret Test
Materials:
1% of alanine and 5% of egg white or albumin for the positive control
Deionized water, as negative control
Biuret reagents
Dry test tubes
Water bath
Pipettes
Reagents:
Biuret reagent is usually made up of copper sulphate, Sodium hydroxide and sodium tartrate, which is also known as Rochelle salt. It also contains a reagent named Biuret which is very important for this Biuret protein assay.
Preparation of Biuret Reagent
Biuret reagent is usually formed by mixing sodium hydroxide with a solution of copper sulphate which turns it into alkaline. Then the biuret reagent is yield as 1000 ml by the following steps.
First, 500 ml of distilled water is taken and it is dissolved with pentavalent copper sulphate of 1.5grams and further with sodium potassium tartrate of 6 grams.
Sodium potassium tartrate contains chelating substance that helps in stabilising the ions of copper.
Then 375ml of molar hydroxide is taken and both the solutions are mixed in the volumetric flask.
Hence finally 1000ml is made by pouring a distilled water into the flask.
Biuret Test Procedure
Initially 3 dry test tubes are taken.
1 to 2ml of test solution, albumin and the deionised water are added into the test tubes.
Then 2 ml of Biuret reagent is added in each of the test tubes.
The test tubes are shaken well and it is left undisturbed for 5 minutes.
And finally, the colour changes are observed.
Biuret Test Observation and Interpretations
Observation Interpretation No change in colour Absence of proteins Solution turns from blue to violet Presence of proteins Solution turns from blue to pink Presence of proteins Biuret Test Result
In positive controls the colour changes from blue to purple and thus indicates the presence of proteins. However only amino acids and Histidine gives a positive result.
In negative controls there will be no colour change.
Significance of Biuret Test
Protein is usually a complex substance which are formed by thousands of amino acids.
Amino acids are considered as amphoteric electrolytes having a group of carboxyl and amino and acts like an acid and base.
Amino acid consists of one positive and one negative charge and hence these ions are said to be electrically neutral and it does not migrate in the electrical field.
The two amino acid are linked together with a help of peptide bond which yields dipeptide.
The bond is formed between alpha-carboxy group of another amino acid and the alpha-carboxyl group oof the other amino acid by the removal of water molecule.
Peptide bond is formed as the result of condensation reaction. At the same time, three amino acids are linked together but two peptide bonds and are called as tripeptide.
During the formation of tripeptide, the chain elongates and it forms a polypeptide.
Generally, Biuret is a complex compound which is formed when heating urea at 180ºC and results in a condensation of two molecules of urea.
The peptide bond in a Biuret gives a positive result of the test. Biuret test is considered as a generalized test for detecting the proteins and peptides which has more than one peptide bond.
Biuret Test Citations
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Pathogen, Pathogenesis, Pathogenicity: Definition and Examples
Continue ReadingWhat are Pathogens?
According to the norms of the nature, we are all part of the environment, where remaining parts are being filled by microorganisms and other species of animals, insects and plants.
These micro-organisms are classified as infectious and non-infectious organisms. The organisms which cause infections are generally described as pathogens.
They include virus, bacteria, fungi and other protists. Where as the non-infectious organisms includes organisms like Lacto bacilli which plays a very important role in diary industries.
Generally, pathogen refers to “suffering” in Greek terms; which is a characteristic of an organism that causes disease.
Pathogen can also be termed as infectious agent or simply as germ. The term pathogen came into existence in the year 1880s, which is typically used to describe a virus, bacterium, protozoan, or fungi.
In some cases, small organisms such as small worms and tiny insects can spread diseases.
Such types of organisms transmitting diseases is referred to as parasites. However, these pathogens and parasites are in common parlance of causing and transmitting infectious diseases.
Thus, the study involving pathogenic organisms is referred to as microbiology and the study which involves parasites are known as parasitology.
Pathogens uses several mechanisms to invade a host body. There are many principal pathways which have different episodic time frames; however, soil has the longest potential to harbor a pathogen. Diseases that are caused by pathogens are known as pathogenic diseases.
What is Pathogenicity?
Pathogenicity generally refers to the capacity of the pathogens to cause diseases.
Pathogenicity is similar a term to that of virulence in meaning, but some authorities have distinguished this in a qualitive form where as the other is known as quantitative. According to this, an organism is said to be pathogenic or not.
In simple words, pathogenicity is the ability of a pathogenic organism to cause disease.
This ability of the organism to produce disease is characteristic feature of an organism, which they acquire during their effort for surviving in the host.
The host may be either animal or plant or any other species including humans.
Types of Pathogen
Pathogens are of different types and they can spread by various means, but most commonly they spread by means of skin contact, or while transferring body fluids or through contaminated surface contacting.
Some pathogens exist as air borne particles.
The most common type of pathogens are bacteria, viruses and fungi. Diseases caused by viral pathogens are mostly common cold, yellow fever, flu, dengue fever, etc.
At the same time diseases caused by bacterial pathogens includes urinary tract infection, tuberculosis, gonorrhea, etc. and the most commonly caused fungal infections includes thrush, ringworm etc.
How Pathogens are Classfied?
Generally, pathogens are classified into four main categories depending on the classes of pathogenicity relying on the general risk analysis and the assessments which is present in practical and theoretical frame works.
I. Class 1
The species coming under this class should have the following criteria.
They must not be a part of group of which causes diseases in humans or any animals.
They are proven to be safe in the past history under the conditions, which does not sort any kind of restrictions physically despite taking an account that species have difference in virulent strains within them.
The species belongs to this class, but it also has relations with a particular gene which could create pathogenicity in animals and humans. This type of species can be put in an exceptional position in this group depending upon the degree of attenuation.
II. Class 2
The species which belongs to this class causes serious diseases in humans and often transmits within humans while having the important prophylaxis.
II. Class 3
The species belonging to this class has the ability to cause serious diseases but it can be treated with necessary therapies.
IV. Class 4
The species belonging to the class causes serious human diseases which disseminates in the human population and where no adequate therapy exists for this particular disease.
Types of Pathogen
Pathogens are classified into four types commonly as viruses, bacteria, fungi and parasites.
I. Virus
Viruses are made up of a piece of genetic code, namely as DNA or RNA and it is protected by a protein coat around itself.
When the individual is affected with viruses invade the host cells in our body and it further replicates and produces more viruses.
After replication, the new viruses are released from the cells of tends starts multiplying again. The hosts which damages the infected cells.
Some viruses remain dormant for a particular period of time. When this occurs in the host, the affected individual gets recovered from the infections and gets sick again. But antibiotics does not help in killing the viruses, antiviral medications are taken for this kind of viral infections.
II. Bacteria
Bacteria is one of the kinds of micro-organisms which is made up of a single cell. They are found in diverse, having variety of shapes and characteristics.
These pathogens have the capability to live in any type of environment inclusive of the human body.
Not every bacterium has the capability to causes diseases. Some type of bacteria’s plays a beneficial role.
Our body is prone to many kinds of bacterial infections when our immune system gets attacked by the viruses.
This diseased state of our body due to viruses enables the harmless bacteria to become infectious. Usually, antibiotics are used to treat the infections caused by bacteria.
III. Fungi
There are about millions of species of fungal species in the earth. But only 300 species are known as pathogens including the indoor and the outer environmental.
These pathogens often cause infections when they are overgrown. Fungal cells consist of a nucleus and other components and are surrounded by a protective cell wall. This complex structure makes them difficult to kill.
IV. Parasites
Parasites are the organisms which behave like tiny animals which lives in the host and feeds themselves through the host tissues.
Parasitic Infections are more commonly found in tropical and sub-tropical regions. There are many types of parasites which causes diseases in humans. Such type of parasites includes protozoa, helminths and ectoparasites.
Pathogen Citations
- Plastic Circuits: Regulatory Flexibility in Fine Tuning Pathogen Success. Trends Microbiol . 2020 May;28(5):360-371.
- Principles of intracellular bacterial pathogen spread from cell to cell. PLoS Pathog . 2018 Dec 13;14(12):e1007380.
- Pathogen proteases and host protease inhibitors in molluscan infectious diseases. J Invertebr Pathol . 2019 Sep;166:107214.
- Shigella host: Pathogen interactions: Keeping bacteria in the loop. Cell Microbiol . 2019 Nov;21(11):e13062.
- Xanthomonas diversity, virulence and plant-pathogen interactions. Nat Rev Microbiol . 2020 Aug;18(8):415-427.
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Widal Test: Definition, Principle, and Procedure
Continue ReadingWidal Test
Now-a days diagnosis has become the basic clinical practice all over the world. As many types of diseases are affecting individuals, and which is becoming new with its origin day by day, diagnosis is very much important for treating the affected individuals.
Widal test is one such method which is used to diagnosis the enteric fever by assuming the symptoms in the individual.
This test is now no longer performed in the any other developed countries like United states, as enteric fever is considered as an endemic and the resources are limited for the rapid use of affordable testing alternatives.
This method is easy to perform, where as the concerns remain about the reliability of the test.
This test is not specific for typhoid fever, it can also be positively used when the person does not have any other infections.
Enteric Fever
Enteric fever is considered as one of the life-threatening illness which is caused by the bacterium, Salmonella enterica serotype Typhi.
It is transmitted my means of contaminated fecal matter. The symptoms associated with this disease includes high fever, fatigue, headache, abdominal pain, constipation, diarrhea, weight loss and sometimes rashes tend to occur, commonly known as rose spots.
Early diagnosis and treatment of this disease is very much essential because this infection leads to serious complications as such severe bleeding in the intestine, perforation in the intestinal tract, etc., which arises within two days of the infection.
Features of Widal Test
In the year 1896, Georges Fernand Widal invented this test as indirect agglutination for enteric fever or undulant fever.
Here the bacteria causing typhoid fever is mixed with the serum which contains specific antibodies are collected from the individual.
In cases of Salmonella infection, the demonstration of this test results in false results. However, test results have to interpreted carefully in order to account for any history of enteric fever, generally people follow typhoid vaccination and general level of antibodies to get rid of this disease.
Typhi dot is another type of test used to diagnosis the typhoid fever, as salmonella typhi gives false results for widal test, other culture techniques like culturing of blood and urine or feces is being allowed.
Basically, widal test is an agglutination test which helps in detecting the presence of serum agglutin’s in the serum of the patients who has typhoid or paratyphoid fever.
When the facilities for culturing is not available widal test greatly helps in diagnosis the typhoid fevers in the endemic regions.
In this test the patient’s serum is tested for O and H antibodies against the antigen suspensions. On testing the serum against the antigen suspensions, salmonella antibodies start arising in the serum at the end of the first week and it rises sharply during the 3rd week of the endemic fever.
Where as in acute typhoid fever, O agglutin’s are detected. After 6 to 8 days of fever, H agglutin’s are detected after 10 to 12 days from the onset of fever.
It is usually preferable that two set of specimens for performing the test at the interval of 7 to 10 days. Salmonella antigens can be performed in slide and through tube techniques.
Principle of Widal Test
Bacterial suspensions which carry the antigen will agglutinate when exposing them to the antibodies of the salmonella species.
Patients suffering from the enteric infection possess antibodies in their serum that reacts and agglutinates in serial doubling dilutes of kills, or colored salmonella antigens in the agglutination test.
The central theme or principle of this widal test is that if homologous antibodies are present in the serum of the patients it will react with the respective antigens that are injected and forms a visible clumping on the test slides or agglutinations in the tubes.
The most commonly used antigens are H and O.
Procedure of Widal Test: Slide Method
– A drop of positive control placed on the slide in the first reaction cycle and further one drop of isotonic saline is pipetted on the next reaction cycle.
– Pipette one drop patient’s serum in the remaining four reaction cycles.
– One drop of widal test antigen “H” is added to the first two reaction circles.
– The antigens “o”, “H”, “AH”, “BH” are added in the respective order to the remaining circles.
– The contents have to be mixed uniformly over the entire reaction circle using separate mixing sticks, then by slitting the slide gently back and forth any agglutination formed is observed visibly.
Interpretation of Widal Test: Slide Method
Agglutination is a positive signal for the enteric fever which indicates the clinically significant levels of the corresponding antibodies in the serum of the patients.
On the other hand, no agglutination is a negative result and it indicates the absence of the clinically significant levels of the corresponding antibodies in the patient’s serum.
Widal Test: Test Tube Method
In widal tests, generally two types of tubes are being used namely Dreyer’s tube and Felicx tube.
Dreyers tube is used for H agglutination and Felix tube is used for O agglutination. But now a days Kahn tubes are used for both the types of agglutinations.
Procedure of Widal Test: Test Tube Method
Let us take four set of Kahn test tubes and label them in the numeric from 1 to 8 for O, H, AH and BH antibody detections.
First, we have to pipette out 1.9ml of isotonic saline solution the first tube. And then 1.0ml of isotonic saline in the remaining tubes.
Then 0.1ml of serum sample to added to the tube 1 and it is mixed thoroughly. Now transfer the diluted serum from tube one and mix it in the tube two using the same technique as of serial dilution and perform the same in the remaining tubes.
At last, add one drop of the respective widal test antigen in all the tubes and mix well and cover the tubes.
Further incubate the covered tubes at 37degree overnight for approximately 18 hours. Dislodge the sedimentation button gently and observe whether the agglutination takes place.
Interpretation of Widal Test: Test Tube Method
The Patients titre using the widal test antigen suspensions in the highest dilution form shows the visible agglutination results.
The sample which shows the titre of 1:100 or more for the O agglutination and 1:200 or more than that for the H agglutination is considered as clinically significant.
Usually, H agglutination is found as more reliable than the O agglutin. Agglutination usually starts appearing in the serum but the end of the first week which rises sharply in the upcoming 2nd and 3rd weeks and after that it declines.
Widal Test Citations
- Reassessment of the Widal test in the diagnosis of typhoid. Gastroenterology . 1977 Aug;73(2):233-6.
- Evaluation of false negativity of the Widal test among culture proven typhoid fever cases. J Infect Dev Ctries . 2008 Dec 1;2(6):475-8.
- Widal test in diagnosis of typhoid fever in Turkey. Clin Diagn Lab Immunol . 2002 Jul;9(4):938-41.
- Widal agglutination test – 100 years later: still plagued by controversy. Postgrad Med J . 2000 Feb;76(892):80-4.
- Performance of Widal test and stool culture in the diagnosis of typhoid fever among suspected patients in Dar es Salaam, Tanzania. BMC Res Notes . 2019 Jun 5;12(1):316.
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Hardy Weinberg Equilibrium: Definition, Condition, and Equation
Continue ReadingWhat is Hardy Weinberg Equilibrium?
Hardy Weinberg equilibrium explains the genetic variation among the populations which remains constant from one generation to the next without disturbing factors.
In a large random mating population, the allele and the genotype frequencies stay constants in the absence of evolutionary influences from one generation to the preceding generations.
Influences occurring are inclusive of the choices of mating, natural selection, gene flow, genetic hitchhiking, founder effect, meiotic drive, population bottleneck, inbreeding and assortative mating.
Genotype and the allele frequencies are related to each. This law also conveys the genetic drift in a population has been known already.
Taking a gene of a single locus which consists of only two alleles, indicated by A which has its corresponding frequencies and it is termed as f(A) =p and f(a)-1 respectively, then the corresponding genotype frequencies are expected under a limited condition where random mating is;
f(AA)=p2 for the homozygotes AA.
f(aa)=q2 for homozygotes aa.
f(Aa)=2pq for the heterozygotes
The equation of Hardy Weinberg principle can be represented as;
P2+q2+2pq=1
Here the allele frequencies p and q remain constant in absence of all kind of influences, such as mutation, natural selection, genetic drift, etc. from one generation to the another. Thus equilibrium can be reached.
History of Hardy Weinberg Equilibrium
Hardy Weinberg Equilibrium was proposed by two researchers namely G.H Hardy and Wilhelm Weinberg. These two members were actually the pioneers in mathematics, and they illustrated this principle scientifically.
So, this law is commonly referred to as Hardy Weinberg equilibrium, theory or law. Hardy’s thesis paid a central attention to debunk the view which prevailed at the times when dominant allele has a capability to increase in frequency automatically.
Now a days the uncertainty on selection and dominance is not remarkable. In recent times, Hardy Weinberg s frequencies in the genotype tests are applied to evaluate population which stratifies and sorts the random-mating.
Interference of Hardy Weinberg Equilibrium
There are few deductions according to this principle and they are listed below:
Only sexual reproductions take place
Mating occurs randomly
Size of population is indefinitely large
Diploid entities occur
Overlapping of generations do not occur
There will be an equality of frequencies between the alleles in terms of sexes
There will be no trace of gene flow, selection, mutation, migration or admixture.
If there are any changes with regard to the above-mentioned assumptions, it leads to discrepancies from expected outcomes.
The consequences occurring are dependent on the deduction which has been digressed.
The law mentioned in the population have the Hardy Weinberg proportions when the single generation of random mating is carried out in a population.
In some cases, the assumption of random mating is breached, and the particular population will not possess the proportions of Hardy Weinberg’s law.
The most common source of non-random mating is considered as breeding, which leads to a rise in homozygosity of the genes.
Four's of Hardy Weinberg Equilibrium
Breaching of any one of these four assumptions causes the populations to possess a proportions of Hardy Weinberg principle.
However, with time there will be an alteration in a given frequencies.
I. Mutation
Mutation has a mild impact in the frequency of the allele. The rate of mutation occurs in the order of 10-4 to 10-8.
Mostly the modifications in the frequencies of the alleles occurs in this order, even if there is any sturdy selection against the alleles in the given population, recurrent mutation will take care of it.
II. Selection
Selection typically leads to a change in the frequency of the alle and it occurs rapidly. In some kind of selections, the selected one results in equilibrium where is no loss of alleles, which is also said to be as balancing selection, where as in other kind of selections, such as directional selection there will be a gradual loss of the alleles.
III. Size of The Population
If the size of a population is small it leads to the random alteration in the frequencies of the alleles which attributes the sampling effect, commonly known as genetic drift. If the alleles are found in a fewer copy, sampling effects are considered to be significant.
IV. Migration
Migration in two or more population helps in associating the alleles genetically together. Here among the populations, the frequency of allele has the tendency to become more homozygous.
Significantly, a few models of migration in the non-random mating are said to be as Wahlund effect. Hardy Weinberg proportions are invalid in some cases.
Application of Hardy Weinberg Equilibrium
Generally natural populations depict the genetic variations continuously and leads to the alterations in the form of mutations, migration, genetic drift, natural or in sexual selection.
However, Hardy Weinberg Equilibrium provides a mathematical criterion of the population which is non-evolving and that can be compared among the evolving populations.
Over-time if the frequencies of the alleles are noted and estimated for the excepted frequencies, depending upon the values of the Hardy Weinberg law, then the evolution of the population which are driven can be hypothesized.
This law offers a protype, which can be used as a point of organization order to study the population of the genetics in the diploid entities, which also fulfills the assumption of the random mattings, large populations, no mutations, selection or migration, Apart from this Hardy Weinberg model is not applicable to haploid pathogens, in the event of a population which are not found in an equilibrium, one of the assumptions related to this law gets violated.
This suggests that selection non-random mating or migration influences the population, where the case experiments are done and the hypothesis are advanced in order to understand the reason behind the non-equilibrium of the population.
Hardy Weinberg Equilibrium Citations
- A century of Hardy-Weinberg equilibrium. Twin Res Hum Genet . 2008 Jun;11(3):249-56.
- Hardy Weinberg Equilibrium Disturbances in Case-Control Studies Lead to Non-Conclusive Results. Cell J . 2021 Jan;22(4):572-574.
- A note on exact tests of Hardy-Weinberg equilibrium. Am J Hum Genet . 2005 May;76(5):887-93.
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Natural Selection: Definition, Examples, and Facts
Continue ReadingNatural Selection
The word evolution has been mentioned, first in the book named “The Origin of Species”, which was written by Charles Darwin in the year 1859.
He Put forth the concept of evolution during his journey towards the Galapagos Islands. He also noted that, all the living species changes both physically and anatomically over a long period of time for their better adaptation in the developing environment around them, this difference is usually by a natural process in the species which gets adjusts itself accordingly in the way that it could survive.
This concept was commonly known as Natural selection and it was called as Survival of the fittest by Darwin.
What is Natural Selection?
Natural selection is generally defined as the process in which the living organisms adapt themselves or change themselves in response to the environmental conditions.
These organisms are better suited for their lives to tend on the environment which survive longer and produces more offspring’s.
Different conditions incline a specific organism to acquire an adaptive trait, where these traits are passed on to the next generation.
As time passes, these characters will become more common as they are predominantly present over other traits in the population.
Biologically Natural selection is a process in which the living organisms possess particular genotypic characters which makes them better adjustable to the environment that they tend to survive, reproduce and increase their number and which therefore enables them to transmit and perpetuate their essential genotypic characteristics over successful generations.
According to Urry et al, natural selection is nothing but which refers to the differential survival and reproduction among the individuals.
It is a very important mechanism of evolution as when a change is inheritable it leads to take the traits to a population over generations.
One of the basic ideas of natural election is all individuals are naturally variable which means that each one is different in their own way.
These variations exist in an organism, who meets changes more randomly and these changes will be passed to the offspring.
Natural selection occurs when some of the changes helps an organism to survive and reproduce in a better way, causing a gene to become more common in a population over a period of time.
As the environment is continuously changing no organism is constructed perfectly suited or absolutely adapted to its environment.
It will always be selective on certain organisms which possess certain genetic combinations, which makes natural selection as an important driving force in evolution.
Principle of Natural Selection
Let us know about the few principles of natural selection, even if the parents are adapted perfectly to the environmental changes, their offspring tend to change according to the environmental conditions which in turn attempts to thrive the limited resources and to win over the competition along with the other inhabitants.
At these competitive times, the most fitted organism is favorable to produce organisms which adapt to themselves to the organisms.
As a result, these organisms will survive in the adapted environment and it also passes their traits or genes to the next generation.
These variabilities in the traits causes the organisms to be slightly vary in each individual which leads to them to reproduce greatly and create different individuals.
The organisms which do not adapt genetically is not fit to survive and will not reproduce further, as a result, evolutionary line will eventually cease to exist.
Natural selection process causes populations to adapt to their particular environment over time. The individuals in a population inherits the traits which helps them to survive the environmental stressors and to safeguard them from predators and to adapt them according to the availability of food.
Those individuals which are inherited tends to have more offspring’s in the upcoming generations, comparing with their peers.
These traits now allows them to stay effective in surviving and reproducing. As resources are limited in nature, the individuals with favorable traits increases the frequency over generations.
Natural selection is usually described as the differential reproduction. Some organisms which carry the favorable genetic variants tends to increases their survival and have higher rate of successive reproductions comparing with the alternative genetic variants.
Selection happens when there is a difference in their survival, success of mating, fertility and development.
Conditions and Importance of Natural Selection
Through this process of natural selection, favorable traits are transferred from one generation to the other.
It also leads to speciation where one species gives rise to new varieties of species with distinct traits.
Natural selection is considered as an important process, as it drives the process of evolution and helps us in explaining the diversity of life on the Earth.
There are four rules to be followed to process the natural selection. They are Reproduction,heredity, variation-in the fitness of the organism, variations in the individual characters between the members of the population. If these four conditions are met, natural selection results automatically.
Natural Selection Citations
- Natural selection, plasticity, and the rationale for largest-scale trends. Stud Hist Philos Biol Biomed Sci . Apr-Jun 2018;68-69:25-33.
- Natural selection and the maximization of fitness. Biol Rev Camb Philos Soc . 2016 Aug;91(3):712-27.
- Natural selection then and now. Biol Rev Camb Philos Soc . 2010 Nov;85(4):829-35.
- The fundamental theorem of natural selection. J Anim Breed Genet . 2018 Oct;135(6):393-394.
- What is adaptation by natural selection? Perspectives of an experimental microbiologist. PLoS Genet . 2017 Apr 20;13(4):e1006668.
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Adaptive Radiation: Definition, Examples, and Facts
Continue ReadingAdaptive Radiation
Generally, in evolutionary biology, adaptive radiation refers to a type of process in which the organisms are diverged rapidly from an ancestral species to a multitude new form especially when there is a change in an environment and the available resources for them such as alteration in the biotic interactions or new environmental niches.
However, starting from a single ancestor evolution in the speciation and their adaptations in the species shows different morphological and physiological traits.
One of the prototypical examples of adaptive radiation is Galapagos based on finch speciation. It is often known as Darwin’s finches.
What is Adaptive Radiation?
Adaptive radiation is generally defined as the adaptation of an organism that enables them to serve successfully in varying environmental regions.
According to Darwin theory of evolution, all the living organisms change their physical and anatomical structures for a longer period of time for improving their adaptations according to the changing environment.
The starting point of evolution is when organisms wanted to exploit a niche so that they are not able to exist with the same body designs and the structural components.
According to the changing environment organisms started to split themselves and adapts various versions for their better survival.
Else more, adaptive radiation is one of the evolutionary process in which the organism originates from one species in a particular are and radiate to different species at different areas.
The phenomenon of adaptive radiation was first identified by Darwin when he was travelling to Galapagos island. There he observed finches with various types of beaks.
On observing those finches, he concluded that all of them are radiated from the single individuals in the same island from their single ancestor finch.
Where all of these Finches has developed beaks accordingly to the kind of food that are available for them.
Hence it is said that they are evolved from the conventional seed eating finches, which is later known as Darwin’s finches
Cause of Adaptive Radiation
Adaptive radiation most commonly occurs due to major changes in the environmental factors and other physical disturbances.
It helps an organism to spread successfully in the other environmental regions.
Further it also leads to speciation which leads to phenotypically dissimilar and related species.
There are few reasons for the cause of adaptive radiation and they are listed below.
I. Ecological Opportunities
On entering into a new environment which has lot of ecological opportunities, organisms tend to adapt themselves according to it, which results in adaptive divergence.
An adaptive zone is generally an unexploited area which has various ecological opportunities.
Example: Nocturnal flying to catch insects and small flies, grazing on grass while migrating across Savana, swimming on the surface of the ocean to filter the planktons, etc.
Vacant adaptive areas are more commonly found on islands, because only few species inhabit in the islands compared to that of main lands.
When these adaptive zones are empty, they will be get filled by the species which diversifies quickly.
For example: Cichlids of African great Lakes, Darwin’s Finches of Galapagos Islands, Hawaiian honeycreepers, etc.
II. Mass Extinction
When there comes a mass extinction due to major environmental conditions or other physical disturbances, it also leads to adaptive variations with variety of reasons.
Extinction in a particular area produces empty adaptive zones which provides a new opportunity for a species that exists.
For example: After the extinction of dinosaurs, mammals get diversified quickly by exploiting various zone of adaptiveness.
As a result of these extinction competitions, species which remains flourishes.
For example: Mammals which has coexisted with the reptiles, but now they are considerably small so that they can hide and save themselves form great creatures like dinosaurs.
Acquisition of Novel Adaptive Traits
Evolutionary innovations trigger various adaptive radiations.
Evolutionary novelties are the variations in the pre-existing creatures which are known as preadaptation’s. A change in the basic pattern of the certain species produces unique creatures which adapts to a different role.
Examples of such preadaptation’s includes, Feathers wings on birds which are evolved from reptilian scales represents the preadaptation of flight.
Flowers on the plants has speeded up the ability to engage in the sexual reproduction which has turned into a great advantage of terrestrial animals for pollination which increases the reproduction rate.
Amniotic eggs and wings on insects are also some of the examples of proadaptive variations.
Area of Adaptive Radiation
Adaptive radiation can also be defined as an evolutionary process in any of the groups either in plants or animals into a wide variety of types which are adapted to specialized modes of life.
Adaptive radiations are often seen in the closely related groups which has been evolved in a shorter period of time.
A good example that can be sorted for adaptive radiation is in beginning of the Paleogenic era, approximately 66 million years ago of a basal stock of mammalian which are adapted for running, leaping, climbing, flying and swimming.
Other examples that are includes such as Australian marsupials, cichlif fish, Darwin’s finches or Galapagos finches, etc.
Many types of examples for this type of radiation are mostly found in archipelagoes removed from the main land.
In addition to the Galapagos Islands it can also be seen in Hawaiian archipelago along with its several volcanic islands and the relatively small area hosts a great number of plant and animal species are endemic, which means that they are evolved there and cannot be found anywhere.
Almost 90% of the native species of Hawaii island including flowering plants, land mollusks, birds and insects are found to be endemic.
Examples of Adaptive Radiation
Adaptive radiation helps in understanding the biodiversity. The concept of adaptive radiation can be made clear through the upcoming examples,
1. Let us consider a family consisting of about four children. Now these four children’s have a same parents and origin, and they four grow under the same circumstances and on growing each moved in different regions for the better opportunities.
And now, each of them has their own adaptations depending on their environmental conditions and the region they are living and their lifestyles. In this case, lineage splits and radiates different characteristics.
2. Considering another example, where adaptive radiation is different from the development.
Taking an account of Australian Marsupials which are all from a single ancestral stock from which various species has raised.
But according to the given geographical area, several adaptive radiations take place in various species, which gives rise to convergent evolution.
Marsupials are considered as one of the most commonly known examples for the adaptive radiation.
The marsupials have been diverted into different orders and species where each order gets diversified from its order Euaustralidelphia.
Adaptive Radiation Citations
- The tale of the finch: adaptive radiation and behavioural flexibility. Philos Trans R Soc Lond B Biol Sci . 2010 Apr 12;365(1543):1099-109.
- Mega-evolutionary dynamics of the adaptive radiation of birds. Nature . 2017 Feb 16;542(7641):344-347.
- Comparative landscape genetics and the adaptive radiation of Darwin’s finches: the role of peripheral isolation. Mol Ecol . 2005 Sep;14(10):2943-57.
- Cranial shape evolution in adaptive radiations of birds: comparative morphometrics of Darwin’s finches and Hawaiian honeycreepers. Philos Trans R Soc Lond B Biol Sci . 2017 Feb 5;372(1713):20150481.
- Adaptive Radiation Genomics of Two Ecologically Divergent Hawai’ian Honeycreepers: The ‘akiapōlā’au and the Hawai’i ‘amakihi. J Hered . 2020 Feb 5;111(1):21-32.
- Ecological and evolutionary determinants for the adaptive radiation of the Madagascan vangas. Proc Natl Acad Sci U S A . 2012 Apr 24;109(17):6620-5.
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Miller–Urey Experiment: Results, Conclusion, and Definition
Continue ReadingMiller Urey Experiment
At the time of 1950s in America, there was much speculation about outer space travel. The president of Unites States at that time named Dwight D. Eisenhower send a satellite in orbit in 1957-1958, known as International Geophysical Year.
But unfortunately, in a demonstration of cold war rivalry, the Soviet Union was the first to launch Sputnik, again on the ground, American researchers, undergone a set of experiments to understand a possibility of life in extraterrestrials, and the origin of life on earth.
Thus, the elegant and famous set of observation was Miller Urey experiment, which was undergone by a graduate student Stanley Miller and a Biochemist Harold. C. Urey at Chicago University in the year 1953.
The success of their spawned the scientific subspecialty of exobiology. Exobiology is nothing but a speculative study of life forms beyond the earth.
Purpose of Miller Urey Experiment
When Miller and Urey began their research to understand about the origins of life on earth, they first observed themselves, that they knowledge on two things first the history of earth including the chemical components present in the atmosphere, the amount of sunlight, and water and then about the chemical properties between the living materials.
However, Oparin gave the basis of their ideas about the primordial earth. Miller has also said in an experiment that earth has a status of reducing atmosphere, as all of the outer planets that is present in our solar system such as Jupiter, Saturn, Uranus and Neptune which are all similar as of Earth in their atmospheres.
The discovery of double helical structure of the DNA by Watson and Crick helped Miller and Urey understand about the chemical nature of the Living material.
Where the Watson and Crick discovered the DNA, which is made up of a sequence of nucleic acids which codes for specific amino acids, which is considered as the building blocks of proteins.
From this Miller and Urey concluded that life begin at a minimum amino acids present.
What was Miller Urey Experiment?
The Miller Urey experiment was the first attempt to explore the ideas scientifically based on the origin of life.
The main concept of this experiment is to test the idea of a complex molecules of life which arises on our younger planets through simple and natural chemical reactions.
The building blocks of life have been characterized in the early 19th century. Depending on how the molecules are produced, prime interests to the origin of life are considered.
Two major achievements are given, the one is in the year 1850, where Adolf Strecker succeeded as the first in synthesizing the amino acid in a laboratory as amino acid alanine from a mixture of acetaldehyde, ammonia and hydrogen cyanide.
After few years, in 1861, Alexandr Butlerov, attempted and succeeded in first laboratory synthesis of mixture of sugar from alkaline catalyst.
Even these discoveries were considered as interesting and an appreciable one, they are not related to life problems.
Hence progressing a little improvement in a scientific description, the origin of life was introduced by Ivanovich Oparin.
As Oparin introduced the concept of chemical evolution, which can be seen in Darwin theory of evolution, this concept related to life stood as successive result of spontaneous chemical reaction which produce increasing complex structure of chemicals.
He suggested that such chemical evolution takes place only within an oxidizing atmosphere of the early earth.
Then further, he made modification in his early suggestions and concluded that early atmosphere to a high reducing environment.
As such similar ideas were proposed by English biologist John Haldane who mentioned Prebiotic soup, where the evolution of chemicals takes place.
Oparin and Harold ideas were expressed the experiments in a theoretical level only the conformation for this experiments were given by Miller and Harold Clayton Urey who conceived and built an experiment to stimulate a putative Primitive earth environment.
The Real Miller Urey Experiment
In this experiment a gaseous mixture of hydrogen, methane, ammonia and water were exposed to electrical discharge which stimulates a storm of lightening.
Then this mixture was connected to a bulb which was filled with liquid water that can be heated.
Then it was observed ed that 15 percentage of carbon present in the mixture present as methane was converted into simper carbon components such as formaldehyde and hydrogen cyanide.
These compounds are then combined to a simple form of molecules such as formic acid and urea and some other complex molecules that contains carbon-carbon bonds including those of amino acids, alanine and glycine.
As a result of these processes, the end product was large number of organic molecules containing several amino acids.
Hence these experiments became s experiments proof for the theory of chemical evolution and it has also shown us the chemistry between simple molecules, which are found abundant in the atmosphere primitive to the earth and which leads to the synthesis of vital components which leads to the formation of earth.
Miller Urey Experiment is Not Conclusive
This experiment was a great achievement as they showed the primitive and important biotic components which are abiotically synthesized in the environment and stimulating natural conditions.
But it is not yet been concluded and still many researches are under progress as there are several findings which proves that this experiment is wrong.
Miller Urey Experiment Citations
- From Anodic Oxidation of Aliphatic α-Amino Acids to Polypeptides by Quantum Electrochemistry Approach: Beyond Miller Urey Experiments. J Am Chem Soc . 2019 Sep 11;141(36):14230-14238.
- Conducting miller urey experiments. J Vis Exp . 2014 Jan 21;(83):e51039.
- Theory of chemical evolution of molecule compositions in the universe, in the Miller Urey experiment and the mass distribution of interstellar and intergalactic molecules. J Theor Biol . 2020 Feb 7;486:110097.
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Satellite DNA: Definition, Types, and Meaning
Continue ReadingSatellite DNA
We all know that Eukaryotic genomes are composed of a large number of different classes of the repetitive sequences of the DNA.
It is found either in an arranged tandem or in a dispersed manner. Satellite DNA consists of a repeated sequence.
This region usually encodes for the proteins and some enzymes.
The region which shows a high degree of polymorphism among the population or between the two different organisms is referred to as the Satellite region or Satellite DNA.
This property can be used for paternity testing where the offspring’s and the parents have the same degree of polymorphism.
Features of Satellite DNA
Satellite DNA consists of a large array of tandemly repeating non-coding DNA.
Satellite DNA is one of the main components of the active centromere and it also forms the main structural constituent of the heterochromatin.
Satellite DNA refers to the phenomenon where the repetitions of short sequences of the DNA tends to produce a frequency difference in the bases adenine, cytosine, guanine, and thymine, and thus it has a different density from the bulk DNA and it forms a second or satellite band when the genomic DNA is separated in a density gradient.
Sequences that have a greater ratio of adenine and Thymine displays as a lower density whereas the greater ratio of Guanine and Cytosine displays a higher density than the bulk genomic DNA Satellite DNA is present in the heterochromatin region of the chromosomes. Or in the tightly packed regions of the chromosomes, such as centromeres or telomeres.
Sometimes the euchromatin region, which is also known as an active region of the genome contains the Satellite DNA.
Though satellite DNA has been known as non-coding, as it does not encode proteins. Recent evidence ensures that some of the satellite DNA undergoes transcription.
Structure of Satellite DNA
Satellite DNA consists of an array of tandem repeats which are arranged side by side. These repeats are small as 1 to 2 base pairs long or sometimes long as 10 to 60 base pairs.
The short tandem repeats are called microsatellites or simple sequence repeats, whereas the long tandem repeats are called minisatellites or variable number tandem repeats.
The regions that are present between the two simple sequence repeats are known as inter simple sequence repeats (ISSRs).
The presence of a large number of repeats results in a high mutation rate in the satellite DNA.
However, it is also said that most of these sequences do not code for the proteins, which determines the high mutation consequences rate as low and hence there will be no selection pressure against it.
Why Was It Named as "Satellite DNA”?
Usually, the density of the DNA can be calculated by using the density gradient centrifugation. When the solution present in the DNA is spun at a very high speed in a rotational movement, the sediments in the DNA are in a density-dependent manner.
Thus, when the density of the DNA was determined by using this process, it has been found that satellite DNA formed a second satellite band which gets separated itself from the other DNAs.
The density of DNA is considered as a function of its base sequences and the satellite DNA is highly repetitive and has a reduced characteristic density compared with the rest of the genome. Hence it is called Satellite DNA.
Fuction of Satellite DNA
Even if the satellite DNA is said to be a part of other DNAs, which occupies the genomes wholly like junk or selfish DNA, it does not have any important functions in maintaining the fittest of the organisms.
However, they perform some biological activities as follows.
• Satellite DNAs often reside in the centromeric and pericentromeric regions and they help in regulating the function of the centromere.
• These DNAs are also involved in the formation of heterochromatin. Periodic distribution of adenine-thymine leads to the formation of curved DNA and satellite DNA with its adenine-thymine-rich regions, which is considered to be important for the package of DNA in the region of heterochromatin.
• However, transcripts of satellites have been found in RNA which are mostly in invertebrates, vertebrates, and also in plants, where they are transcribed at a particular region of the developmental site in certain cells and tissues.
As the sequences in satellite DNA are highly diverse and variable, sequence-specific regulatory signals are regulated in the satellite DNA which helps in bringing the fine expression of the gene.
Application of Satellite DNA
The short sequences of the DNA stretch in the satellite DNA and it varies across each individual.
These differences between individuals in length and sequences of the satellite DNA are unique depending upon the species.
This uniqueness of satellite DNA helps in identifying and exploiting each individual based on the DNA map.
This technique is most commonly called DNA fingerprinting which helps in identifying the criminals, crime scenes, the identity of the individuals, and it is also mostly used in paternity tests and in diagnosing genetic disorders.
Satellite DNA Citations
- Satellite DNA-like repeats are dispersed throughout the genome of the Pacific oyster Crassostrea gigas carried by Helentron non-autonomous mobile elements. Sci Rep . 2020 Sep 15;10(1):15107.
- α satellite DNA variation and function of the human centromere. Nucleus . 2017 Jul 4;8(4):331-339.
- Epigenetic Reprogramming of Pericentromeric Satellite DNA in Premalignant and Malignant Lesions. Mol Cancer Res . 2018 Mar;16(3):417-427.
- Satellite DNA in the karyotype evolution of domestic animals–clinical considerations. Cytogenet Genome Res . 2009;126(1-2):12-20.
- Alpha satellite DNA biology: finding function in the recesses of the genome. Chromosome Res . 2018 Sep;26(3):115-138.
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