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Drosophila melanogaster (Fruit Flies): Overview and Life...
Continue ReadingDrosophila melanogaster
Drosophila melanogaster, which is commonly known as fruit fly and comes under the family Diptera.
It is mostly seen in all regions, where it flies above the fruits and undergoes its life cycle mostly in ripened fruits such as banana.
This is mostly used as a specimen in biology to undergo a study or research in its lifecycle.
It is also used in the field of genetics, pathology and microbiology for research purposes.
Drosophila melanogaster is most commonly used in the field of research as it has a shorter life span and also consisting of only four pairs of chromosomes, and it produces a greater number of off springs in a quitter period of time.
It is known as the African species having all the non-African lineages.
More than a research specimen it is generally a common pest or insect in restaurant, home and in road side food stalls.
Scientific Classification of Drosophila melanogaster
Kingdom : Animalia
Phylum : Arthropoda
Class : Insecta
Order : Diptera
Family : Drosophilidae
Genus : Drosophila
Species : D. melanogaster
Physical Characteristics of Drosophila melanogaster
Drosophila melanogaster is considered as a wild type of flies, and they are usually colored with yellow and brown along with black transverse rings in the region of their abdomen.
The eyes are brick red in color. And this color is due to the presence of pigments xanthommatin.
These flies have their sexual dimorphism such that females have their backs longer than males.
Males have dark rounded short backs. However, they are easily distinguished; as males have their abdomen darker than females and they also contain spiky hair around their reproductive regions.
These flies are also capable of sensing air currents which makes their hair move along the air currents and as well their eyes are also sensitive to intense light, so that they are away from predators when a shadow falls on them.
Life Cycle of Drosophila melanogaster
Generally, these flies have a growth range of about 50 days from the stage of egg to death.
However, the development depends upon the temperature, humidity and other notable factors.
Considering the shortest growth rate i.e., from egg to adult it is of 7 days, and the temperature noted here is of 28ºC.
Under increased temperature and at crowded areas the development of these flies increases but it results in smaller flies.
Life cycle of Drosophila melanogaster with stages is shown below
Where as Drosophila melanogaster is an holometabolous insect, which means that it has the capability to undergo full metamorphosis.
The life cycle of Drosophila melanogaster is divided into four stages as embryo/ egg, larva, pupa and adult.
The eggs hatch after half a day that is from 12 to 15 hours of laying which are about 0.5 mm in its size.
The larva which comes out of the embryo has its duration of about 4 days, during this larval stage mounting undergoes twice which results in instars as second and third instar.
During these stages they feed on decomposed matter such as decayed mushrooms, microorganisms and in fruits and enters through the pupal stage where it undergoes metamorphosis for 4 days at 25º C and after this stage come the adult fly.
Reproduction in Drosophila melanogaster
Males Drosophila melanogaster perform a behavioral pattern to attract female Drosophila melanogaster, where males place themselves extending their wings horizontally and starts singing a courtship song by vibrating their wings, then male make their position beyond the female’s abdomen and undergoes copulation.
If females are not interested, they kick the males out.
During copulation males transfer their hundreds of long sperm cells into females, then females store their sperm cells in the seminal vesicle which is present between spermathecae.
Sperm cells compete and undergoes fertilization, then it is being followed by fertilization after several copulation processes.
Female lays about five eggs at a time and almost 400 eggs in its lifetime.
The female mates with first mater throughout its life as it has its sensory neurons in their uterus; which responds to it, by sending signals to the hypothalamus.
Why Drosophila melanogaster is a Model Organism in Genetics?
Drosophila melanogaster is the most commonly used specimen in the life study of genetics and has its own importance in the field of developmental biology too.
It is used to study the environmental mutagenesis.
These were considered as the first organism to use in research field as fruit flies help in the better understanding of transcription and replication in all living eukaryotes inclusive of humans.
Thomas Hunt Morgan, who was the first researcher to use fruit fly in his hereditary experiments, at Columbia University in a Fly room, where the scholars used milk bottle to capture the flies and rear them and as well, they started observing their traits in a microscope which results in better observations.
Only through this study Morgan and his colleagues found out the basic theories and principles of heredity such as gene mapping, epistasis, multiple alleles and sex-linked inheritance.
They are being used since the historical period to study the patterns of inheritance and to know about mutagenesis particularly about environmental mutagenesis.
There are several valuable reasons why we use these flies in laboratory and few of them are:
There is no need for any large culture mediums or equipment’s to carry out experiments with them.
It can also be anesthetized just by giving ether or carbon dioxide as it does not require any medications or vaccines.
Its morphology can be read easily in anaesthetized flies.
Since it has a short life span it helps us to read the mutations and hereditary variations that it undergoes genetically for generations.
It has also had the capability to produce more individuals at a short period of time.
It can also be cultured easily without spending any funds against it.
Females can also be identified easily as, virgin or not and thus helps in experimenting cross genetic techniques.
Where as the mature larva contains a giant chromosome in their salivary glands which is also known as polytene chromosomes.
It also has a puff like structure in the center which helps us to identify the region where transcription takes place.
These flies show its developmental period in a shorter sequence of time. So, it is very helpful in reading developmental biology.
Citations
- Drosophila melanogaster as an experimental organism. Science . 1988 Jun 10;240(4858):1453-9.
- Drosophila melanogaster: a model organism for controlling Dipteran vectors and pests. J Enzyme Inhib Med Chem . 2015 Jun;30(3):505-13.
- Drosophila melanogaster, a new model for exercise research. Acta Physiol (Oxf) . 2019 Nov;227(3):e13352.
- Drosophila melanogaster as a model organism of brain diseases. Int J Mol Sci . 2009 Feb;10(2):407-40.
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Mitochondrial Electron Transport Chain : Cellular Respiration
Continue ReadingMitochondrial Electron Transport Chain
Electron Transport chain is a series of catalysts with rising redox potential.
The basic mechanism involves collection of the reduced equivalents either hydrogen atom or electrons from the substrates and transferring them in a sequential order to get oxidised with the oxygen molecule resulting in formation of water and energy in the form of ATP.
The whole process is also called as redox reaction or respiratory chain.
The electron carriers are assembled in the form of chain within the four membrane-bound enzyme complexes, which are embedded in the inner mitochondrial membrane.
The main advantage of this system is that the electrons transports in a stepwise manner from substrate to oxygen, thus, generating enthalpy slowly in a systematic way preventing sudden burst of energy making the process efficient and well controlled.
Component of Electron Transport Chain
The electron transport chain is composed of:
A. Hydrogen and electron carriers
B. Four membrane-bound enzyme complexes
A. Hydrogen and Electron Carriers of the Electron Transport Chain
1. Nicotinamide Adenine Dinucleotide (NAD): It is a co-enzyme that carries hydride ion (H-) and thus known as a hydride carrier.
It gains 2 hydrogen atoms from the substrate of Citric acid cycle like isocitrate, malate, B-hydroxy acyl CoA and B-hydroxy butyrate and form NADH molecule.
In the process, one electron releases which reduces NADH to NADH+ while passing its hydrogen to flavoprotein containing FMN and iron sulphur protein (FeS).
2. Flavoproteins (FAD and FMN): In the meanwhile, flavoproteins like FAD and FMN both serves as hydrogen acceptor wherein they tightly bound the hydrogen atom.
Thus, directly preventing its reduced form to react with oxygen.
In general, the types of flavoprotein receiving hydrogen passes them to coenzyme Q.
For example, flavoprotein Fp1 receives 2 hydrogen atoms from reduced NAD+, while flavoprotein Fp2 receiving the same from various substrates like succinate, acyl CoA and choline.
3. Ubiquinone: It is also known as Coenzyme Q that contains quinone ring. Coenzyme Q is the most common ubiquinone that shows similarity with vitamin K.
It is lipid soluble with small molecular size thus responsible for free mobility of the molecule in the inner membrane of mitochondria.
It is the basic carrier of the hydrogen atoms, wherein ubiquinol carries 2 hydrogen atoms while semiquinone carries only one.
These molecules connect flavoprotein with cytochrome b, where flavoprotein carries 2 hydrogen atoms while cytochrome b carry one.
Reduction of coenzyme Q leads to passage of electrons to cytochrome b while releasing 2H+ into the mitochondrial matrix.
The enzymes responsible for the oxidation of ubiquinol involves:
a): Conduction of electrons to cytochrome c is mainly responsible by ubiquinol (coenzyme Q) dehydrogenase along with coenzymes cyt b, FeS protein and cyt c1.
b): Another further transfer from cyt c to oxygen is carried out under the presence of cytochrome oxidase along with cyt a and cyt a3 as coenzymes.
4. Cytochromes are mainly responsible to carry electron from coenzyme Q to oxygen. Thus, exhibits the important role of electron carrier.
They are categorized with the letter a, b and c.
The core molecule for all the cytochromes are haemoproteins however they diverge in their redox potential.
The iron of cytochrome frequently changes their state from oxidation (Fe3+; ferric state) to reduction (Fe2+; Ferrous state) during their normal physiologic action, while that of haemoglobin remains in the reduction state.
Being mobile components, both coenzyme Q and cytochrome c transport reduced equivalent from the other fixed components.
5. Iron Sulfur Clusters(FeS): One additional component found is iron sulfur proteins also known as FeS or non-heme iron.
It is often related with flavoproteins and cytochrome b wherein iron is interchangeably exchange between flavoprotein and cytochrome b resulting in redox reaction.
B. Enzyme Complexes of the Electron Transport Chain
In the inner mitochondrial membrane four enzyme complexes are arranged which transport electrons. The following are the enzyme complexes observed:
Complex I known as NADH dehydrogenase (NADH-ubiquinone oxidoreductase) It is a flavoprotein wherein FMN and FeS protein are the coenzymes.
It facilitates transport of hydrogen atoms from NADH to ubiquinone in the form of NADH+ H+.
Complex II is known as Succinate dehydrogenase (succinate-ubiquinone oxidoreductase).
It is also a flavoprotein wherein FAD and FeS protein are the coenzymes.
It transfers hydrogen atoms from succinate to ubiquinone.
Complex III is known as Ubiquinol dehydrogenase (ubiquinol-cytochrome c oxidoreductase).
It facilitates transport of electrons from ubiquinol to cytochrome c with the help of coenzymes cyt b and cyt c1.
Complex IV is known as Cytochrome oxidase (cytochrome-oxygen oxidoreductase).
It facilitates transport of electrons from cytochrome c to oxygen with the help of coenzymes cyt a and cyt a3.
Moreover, there is a fifth complex (Complex V) known as ATP synthase and is facilitates the conversion of ADP to ATP using inorganic phosphate.
Electron Flow in Electron Transport Chain
The oxidation of substrates with the help of NAD+ or FAD results in production of hydrogen atoms that can pass into the electron chain transfer which further successfully transferred to oxygen to generate energy and water.
The hydrogen atoms cannot be accepted directly by the cytochrome b.
Thus, Coenzyme Q ionized the hydrogen atoms to release hydrogen ions and electrons.
The electrons will reduce the heme group from the cytochrome B, with this starts the transfer chain of electrons from cyt c1, cyt c, cyt a to cyta3.
Finally, the electrons are transported with the help of cytochrome oxidase towards oxygen to form ionic oxygen.
ATP Yield in Electron Transport Chain
The ATP count varies with the catabolism of glucose. Moreover, FAD+ molecules can transport fewer ions resulting in fewer ATP molecules.
In addition to this, the intermediate components of glucose can be used for different purposes resulting in variation in the ATP count.
Summary of Electron Transport Chain
The electron transport chain plays significant role in the aerobic respiration where the free oxygen accepts the last electron produced after glucose catabolism as a result from intermediate compounds.
The structural configuration of electron transport chain showed four large, multi-protein complexes penetrated in the inner membrane of mitochondria along with this 2 small diffusible electron carrier are present transferring electrons between them.
During the transfer of the electrons, small amount of energy is lost against the chemiosmosis.
Thus, high-energy electrons are donated by the NADH or FADH to compensate the energy to finish the chain.
Water and ATP are the end products of the electron transport chain.
Moreover, various intermediate products of the tricarboxylic acid cycle can be averted into the anabolism of other biochemical molecules which may serve as the benefactor for glucongenesis.
Electron Transport Chain Citations:
- Mitochondrial electron transport chain: Oxidative phosphorylation, oxidant production, and methods of measurement. Redox Biol . 2020 Oct;37:101674.
- Respiratory metabolism: glycolysis, the TCA cycle and mitochondrial electron transport. Curr Opin Plant Biol . 2004 Jun;7(3):254-61.
- The mitochondrial respiratory chain. Essays Biochem. 2010;47:1-23.
- Bacterial electron transport chains. Annu Rev Biochem . 1988;57:101-32.
- Kinetic modeling of the photosynthetic electron transport chain. Bioelectrochemistry . 2001 Jan;53(1):35-53.
- Electron transport chain defects in Alzheimer’s disease. Neurology . 1995 Mar;45(3 Pt 1):599-600.
- Bioflavonoid effects on the mitochondrial respiratory electron transport chain and cytochrome c redox state. Redox Rep . 1999;4(1-2):35-41.
- Electron transport in xanthine oxidase. A model for other biological electron transport chains. Biophys J . 1976 Aug;16(8):939-51.
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Monocistronic mRNA: Definition, Importance, and Examples
Continue ReadingWhat are Monocistronic mRNA?
Monocistronic mRNA is a mRNA that encodes just a single protein and all eukaryotic mRNAs are monocistronic.
The improvement of the develop monocistronic eukaryotic record includes a few diverse handling steps.
Heterogeneous nuclear RNA (hnRNA) refers to the large pre‐mRNAs of various nucleotide sequences transcribed by RNA Polymerase II.
hnRNA transcription is only a small portion of the transcription which occurs in the nucleus.
Up to 90% of the transcription is for the production of rRNA. But if we limit our discussion to hnRNA some important observations can be made.
First, the complexity of the hnRNA is 4 to 10 times greater than that of the mRNA. This suggest two possibilities.
One, we already know and that is that splicing of genes reduces the size of the final mRNA product in comparison to the original transcript. But this does not account completely for the differences in complexity.
Monocistronic mRNA Features
The majority of the difference appears to be accounted for by destruction of hnRNAs before they develop into mature mRNAs.
hnRNAs are a broad class of products:
• Average size – 8000 – 10,000 bases
• Range – 2000 – 14,000 bases
Since the mean mRNA length is 1800-2000 bases, a sustainable amount of cutting must occur. hnRNA doesn’t really exist in the core as bare RNA however is really connected with protein.
This complex is assigned hnRNP and is called heteronuclear ribonuclearprotein.
hnRNP is related with the nuclear matrix. Since chromatin is connected to the nuclear matrix it appears to be intelligent that the essential transcript will likewise get appended to the matrix soon after transcription.
Processing of Monocistronic mRNA
The lifetime of hnRNA is very short generally from one minute to one hour and no more. The initial phase in handling is the expansion of a cap.
The cap is a 5′ methyl guanosine that is added following the beginning of transcript. Capping happens so rapidly that we seldom see the original 5′ base of the message.
The linkage between the 5′ methyl guanosine isn’t the commonplace 5′- 3′ linkage yet is a 5′- 5′ linkage. The reaction is catalyzed by the enzyme guanylyl transferase.
The guanosine that is attached is consistently methylated at the 7 situation of the guanine base (7mG). This is called cap 0.
Likewise, a methyl bunch is added to 2′- OH of the first base in the mRNA. This is catalyzed by 2′- O-methyl-transferase, and this methyl group is alluded to as cap 1.
Other methylations can takes place, however we will not think about them. About 25% of hnRNA in the end develops in polyadenylated mRNA.
Not all mRNAs are polyadenylated. The histone mRNAs are a remarkable exemption for the standard. In the event that an inhibitor of polyadenylation is added to a response hnRNA isn’t changed over into mRNA.
In this way polyadenlyation is a prerequisite for mRNA to show up.
End of transcription isn’t perceived in any way. One succession that is invariant in eukaryotic mRNA is the sequence 5′- AAUAAA-3′ that is seen around 10-30 bp upstream of the poly A tail.
The inquiry that this raises is whether this sequence is needed for polyadenylation. Erasures or mutation of this sequence will kill polyadenylation.
Yet, astounding, point mutation incredibly decreased the quantity of molecules that are divided.
In any case, those that are separated are polyadenylation. Consequently, this sequence is by all accounts needed for cleavage of the essential transcript.
The poly-A tail is added by the compound poly(A) polymerase.
Monocistronic mRNA Characteristic
Monocistronic mRNAs are the standard mRNAs in eukaryotic cells are perpetually monocistronic, and the size of the mRNA is normally corresponding to the length of the encoded protein.
This is genuine likewise of most plant and animal viral mRNAs, despite the fact that there are, among viral messenger, a few exemptions for the monocistronic rule.
These mRNAs are basically polycistronic: they encode at least two overlapping proteins. Anyhow, in every such case, save one, interpretation is restricted to the 5′- proximal cistron.
(The solitary archived special case is simian virus 40 late 16 SmRNA, in which the 62-aminoacid “agnoprotein” is encoded up-stream from capsid protein VP1 and the two proteins are translated.
These mRNAs are in this manner adjust to the standard for eukaryotes in that they are practically monocistronic. Few eukaryotic mRNAs comprise a third category.
These mRNAs encode and express two proteins. Much of the time, these outcomes from commencement at the first and second AUG trios – interestingly with most of eukaryotic mRNAs.
Monocistronic Rule
The 5′- proximal AUG works as aninitiator codon. Considering the scarcity, they present just a minor inconsistency to the monocistronic rule.
The monocistronic rule for gene expression in eucaryotes states not just that a single mRNA coordinates synthesis of a single protein yet in addition that the protein encoded nearest to the 5′ end is the one that gets expressed.
This remains constant for the entirety of the naturally occurring viral mRNAs recorded, just as for misleadingly constructed messengers that encode two proteins.
The 5′- terminal restriction is imposed not by the structure of eukaryotic mRNAs yet rather by the properties of eukaryotic ribosomes.
This was astutely shown by brooding wheat germ ribosomes with a polycistronic mRNA from bacteriophage lambda.
Though E.coli ribosomes promptly translate the first and second cistrons in that message, wheat germ ribosomes decipher just the first.
Inability to decipher down-stream cistrons suggests that eukaryotic ribosomes can neither tie straightforwardly to internal initiation sites nor reinitiate at a subsequent cistron in the wake of crossing the first.
Plainly, eukaryotic ribosomes work under restrictions that don’t happen in procaryotes.
The failure of eukaryotic ribosomes to start at destinations in the inside of a message implies that eukaryotic cells can’t organize synthesis of a bunch of proteins by grouping the genes behind a single transcriptional promoter.
Polycistronic transcripts, which are the transcendent regulatory device utilized by procaryotes, won’t work in eucaryotes.
Taking into account this restriction, it is fascinating to ask what compensatory mechanism eukaryotic cells have formulated to organize gene expression.
Eukaryotic genes are sometimes fused, hence creating, in lieu of a polycistronic mRNA, a “polyprotein” which is gotten from a single longsome cistron.
Monocistronic mRNA Example
Tryptophan synthetase is one such model: the alpha subunit (Mr28,727) and 32 subunit (Mr42,756), which are encoded by isolated genes in E.coli, are fused in S. cerevisiae to form a bifunctional protein of Mr76,000.
Different instances of fused genes encoding multifunctional proteins are the arom gene cluster in Neurospora, which incorporates five enzymes associated with the polyaromatic biosynthetic pathway, and the his4 gene in S.cerevisiae which encodes a trifunctional protein.
Maybe the most noteworthy model is mammalian unsaturated fatty acid synthetase (Mr240,000), which relates to a set of 7 individual polypeptides in E.coli (2%).
Albeit the reasoning behind gene combination is more managable to speculating than to experimentation, it is conceivable that fusion of genes makes up for the failure of eukaryotic ribosomes to utilize polycistronic transcripts for the coordinate synthesis of polypeptides.
Monocistronic mRNA Citations
- Translation of the RNAs of brome mosaic virus: the monocistronic nature of RNA1 and RNA2. J Mol Biol . 1976 May 5;103(1):77-88.
- Gene Gangs of the Chloroviruses: Conserved Clusters of Collinear Monocistronic Genes. Viruses . 2018 Oct 20;10(10):576.
- Identification of novel monocistronic HTLV-1 mRNAs encoding functional Rex isoforms. Retrovirology . 2015 Jul 2;12:58.
- A promoter within the E6 ORF of human papillomavirus type 16 contributes to the expression of the E7 oncoprotein from a monocistronic mRNA. J Gen Virol . 2003 Dec;84(Pt 12):3429-3441.
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Seed Germination: Definition, Process, Methods, and Major...
Continue ReadingWhat is Seed Germination?
Seed Germination is defined as one of the vital process by which all the species of plants got generated from a single seed and how it gets adapted to a particular environment and grow itself as a crop or as an herb or as shrub or a tree.
The best example that we come across our day-to-day life is sprouting of pulses in our kitchen or young plants developing in our kitchen garden.
Process of Seed Germination
When we sow a seed in a mud, first the seed starts absorbing water from its outer environment or directly from the soil, which results in bulging of seed and its seed coat gets moisture and becomes very vulnerable at a particular temperature.
This stage of the seed which can be seen from one to two days of sowing is commonly referred to as imbibition.
It further resumes its growth process by activating several enzymes and starts its respiration and initiates the production of proteins and stores nutrients in it by metabolising those necessary proteins.
Hence, it is said that sprouts are rich in proteins.
This stage of the plant is generally referred to as lag phase. Then the seed coat starts rupturing and gives rise to a small radicle, which later forms the primary root of a plant.
This helps the plant to absorb the underground water along with other nutrients present in the soil and helps in further growth of the plant.
The slowly starts growing the plumule of the plant which later develops into the stem portion of the plant.
As days move on seeds modify itself as seedling, then plumule starts growing upwards giving rise to leaves and other floral parts of the plant.
Optimum Condition for Seed Germination
Not all the seeds have the capability to grow at any conditions we sow, certain seeds grow only at certain conditions and certain soil and climatic conditions.
The things that are necessary for a plant to grow in a good condition are listed below.
A. Water
As every living organisms’ water is the most vital component for a seed to germinate.
Though some seeds do not require much water for their growth they need at least a minimal quality of water at certain intervals.
It depends on the dry weight of the seed. As discussed above the seed starts its germination process by absorbing water which is necessary for the nourishment of the embryo by providing dissolved oxygen and soluble supplements for their growth.
The dissolved oxygen helps the seed coat to become softened and converts the seed into a sapling by rupturing the seed coat.
B. Oxygen
As water oxygen is also very much important for the seed growth, which is obtained through the water in a dissolved form or through the porous soil.
But the deep buried seeds are not capable to use the oxygen from the soil pores.
Oxygen is vital for the metabolic process of the seed in terms of aerobic condition.
C. Temperature
If the seed wants to grow in a proper manner without any deficient conditions then the temperature should be maintained at an average of 25 to 30ºC. But in some cases, the seeds need a temperature of 5 to 40ºC.
Hence the temperature varies according the particular regions where they are native to and other environmental factors.
D. Light and Dark Cycle
This depends on the nature of certain seeds, some seeds do not germinate if sunlight falls on them, such kind of seeds are grown in a dark condition and after germination they are brought to the field.
Whereas most of the plant needs sunlight for the germination and throughout their lifetime.
Thus, the seed germination needs all these vital factors and generation of plumule and radicle is said to be completion of seed germination.
Factors Affecting Seed Germination
Factors affecting seed growth or germination may be both internal and external and they are listed below as follows.
Internal Factors
Seed dormancy is considered as one of the important factors in germination process which means that seeds do not germinate if they met any unfavorable conditions during their process of undergoing their growth.
During this period the seed coat which allows the passage of water restricts the water to absorb so that the oxygen and nutrients necessary for their growth is limited.
So that the seeds remain as such without any development. But in some cases, the plant growth regulators help in the growth of the plant.
However, some seeds germinate within a week where as others take their own time to germinate.
External Factors
As mentioned above water, oxygen and temperature are considered as important factors for the germination of a plant.
a. Water
Seed growth gets affected when the water is supplied at higher amount than the needed quantity and also when it is supplied in very low quantity or there is no supply of water.
So, it is important to know the nature of seeds and their adequate flow of water.
b. Oxygen
While the seeds start its germination process it intakes large amount of water than other intervals, so it is checking the availability of oxygen for the growth of the plant.
c. Temperature
Seeds require only the appropriate temperature necessary for their growth if the temperature is more vigorous than needed then seeds starts shrinking and it will die or degenerate.
So, the seed must be sown in optimum environmental conditions by considering the environmental factors.
Seed Germination Citations
- Seed dormancy and germination. Curr Biol . 2017 Sep 11;27(17):R874-R878.
- Seed germination traits shape community assembly along a hydroperiod gradient. Ann Bot . 2020 Jan 8;125(1):67-78.
- Phytochrome Regulation of Seed Germination. Methods Mol Biol . 2019;2026:149-156.
- Seed germination and dormancy: The classic story, new puzzles, and evolution. J Integr Plant Biol . 2019 May;61(5):541-563.
- The biomechanics of seed germination. J Exp Bot . 2017 Feb 1;68(4):765-783.
- Studies on the molecular mechanisms of seed germination. Proteomics . 2015 May;15(10):1671-9.
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Mendel’s Laws of Inheritance : Types and...
Continue ReadingWhat is Mendel's Laws of Inheritance or Mendelian genetics?
Mendelian genetics or Mendelism or Mendelian inheritance is a pack of primary tenets that are affiliated to the relaying of hereditary features from parent organisms to their kids; it is nothing but due to the genetics.
These tenets were originally extracted from the study of Gregor Mendel published in the year 1865 and 1866, which was founded in 1900.
It was originally controversial, however later it became core of classic genetics.
Historical Facts About Mendel's Laws of Inheritance
Credit of laws of inheritance goes to Gregor Mendel, a monk of nineteen century who performed experiments on hybridization in peas (Pisum sativum).
Between 1856 and 1863, he grew and tested around 28,000 pea plants and from this he deduced two generalizations that became famous as Mendel’s Laws of Heredity or Mendelian inheritance.
This is delineated in two sections of the research paper “Experiments on Plant Hybridization”, that was published in the journal in the year 1866.
What is Inheritance?
Inheritance can be defined as the procedure of how a child receives genetic information from the parent.
This process of hereditary is related to the dependence which gives the offspring same trait as of parents.
Inheritance is which is why, the family members have similar and distinctive features.
Why Mendel Choose Pea to Study Genetics?
He chose pea for his experimental procedures because it can be grown easily and are naturally self-pollinating.
Pea plant not only can be self-pollinated but also can be cross-pollinated.
It is yearly plant, ergo, many generations can be followed in less duration of time.
Not only this it also possesses contrasting traits.
Mendel's Laws of Inheritance
The two majors’ experiments done by Mendel to establish the laws of inheritance (Mendel’s Laws of Inheritance) were:
1. Monohybrid Cross Experiment
2. Dihybrid Cross Experiment
During his procedure he found that many features and traits passes to the offspring in a stable way.
These factors are known as genes. Unit of inheritance is nothing but genes.
Mendel’s Experiments
He conducted experiments and contemplated seven major contrasting features in the plants.
Then, he conducted both the experiments to determine the aforementioned inheritance laws.
1. Monohybrid Cross
He took two plants of pea with contradictory traits that is one short and one tall and then crossed them.
It was noticed by him that the offspring’s of the 1st generation were tall and he termed it as F1 progeny.
Then he crossed F1 progeny which yield him tall as well as short plants in the ratio 3:1.
Mendel even did experiment with other contrasting features like green peas vs yellow peas, round vs wrinkled, etc. and he found that the results were the same.
This led to the discovery and the formulation of the laws of Segregation and Dominance.
2. Dihybrid Cross
Mendel in his dihybrid cross trial he took two traits, each having two alleles and then he crossed wrinkled-green seed and round-yellow seeds and noticed that all the first generation progeny (F1 progeny) were round-yellow.
He therefore concluded that the dominant traits were the round shape and yellow colour.
He also self-pollinated the F1 progeny and got 4 different features like wrinkled-yellow, round-yellow, wrinkled-green seeds and round-green in the ratio 9:3:3:1.
Mendel's Laws of Inheritance
Mendel postulated three laws, which are now called after his name as Mendel’s laws of heredity.
1. Law of dominance
2. Law of segregation
3. Law of independent assortment
1. Law of Dominance
When two homozygous individuals with one or more sets of contrasting characters are crossed, the characters that appear in the F1 hybrids are dominant characters and those do not appear in F1 are recessive characters.
The dominant and recessive traits of the genes can be dependent on the enzymatic function of the genes of which dominant genes can make functional enzymes which synthesize active polypeptides or proteins.
On the other hand, the recessive genes (mutant genes) code for incomplete or non-functional polypeptides.
Therefore, the dominant genes make a distinct phenotype which can be expressed even in the heterozygous condition while the recessive cannot make so.
Researchers undertook various cross-breeding experiments to authenticate applicability of law of dominance like Correns on peas and maize, Tschermak on peas, and many others.
They discern plenty of characters in several life form is related as dominant and recessive.
Importance of Law of Dominance
In the hybrid trait the normal characteristics shown by dominant gene reveal significant advantages over the dreadful characters exhibited by recessive gene.
It was noted that diabetes, hemophilia etc. are all traits of recessive characters.
A hybrid person may possess all these characteristic in addition to this recessive gene can persist for next several generations without expressing themselves.
In contrast, there is exception to Law of Dominance which is known as Incomplete Dominance.
Mendel was followed by several scientists in case of blending of characters of two parents.
This trait shows characteristics which are amalgamated from both the parents with both sets of genes which is commonly known as incomplete dominance or blending inheritance.
It is the result of expression of genes partially from the dominant trait and partially from the recessive one.
For example, in four O-clock plant, Mirabilis Jalapa, red (RR)flower plant is crossed with white (rr) colored plant resulting in plant with pink (Rr) color flower.
On self-pollination with pink color flower the ratio of getting red (RR), pink (Rr) and white (rr) is 1:2:1.
2. Law of Segregation (Purity of Gametes)
This law states that when trait of two opposite genes or allelomophs are mixed together the resultant pair stays without being contaminated while gametes separate out from each other and only one enters each gametes.
As a result, two types of gametes are produced from the heterozygote in equal numerosity. 50% of the gametes possess gene T and other 50% possess gene t.
Importance of Law of Segregation
According to cytological studies, the law of segregation holds good to all cases whether it is dominance or no dominance.
Rare biological generalization has made its applicability far out reaching.
3. Law of Independent Assortment
In this law, the study of inheritance of more than one pair of characters is carried our simultaneously, wherein the factors or genes can be sorted independently from its correspondent allele.
Based on the result of dihybrid cross, Mandel formulated Mendel’s Laws: Independent Assortment .
Importance of Law of Independent Assortment
Various cytological studies revealed that those allelomorphs which are assorted independently during cell division, are actually located on different homologous pairs of chromosomes.
However, if the traits for various characteristics are seen on the same homologous pair of chromosomes, these are passed on to the same gamete.
This law fails on its universal applicability.
Biological Significance of Mendel's Laws
Mendel’s work unfolded after 3 decades of his actual work and the laws he mentioned was widely used by various branched for the purpose of scientific evaluation.
Many modern genetic modification was seen like getting rust-resistant and disease-resistant varieties of grains and for breeding high grade variety of horses and dogs.
The science of segregation is the outcome of Mendelism, which deals with the betterment of human race.
Conclusions from Mendel’s Experiments
Genotype is defined by the genetic makeup of the organism while phenotype is defined by its physical appearance.
The genes are transmitted from parents to offspring and is called as allele.
There is a 50% chance of one of the two alleles to fuse with the other parent during gametogenesis when the chromosomes are halved.
When the alleles are the same, they are known as homozygous alleles and when they are different they are known as heterozygous alleles.
Mendel’s law benefited the humankind by generating high grade breed of various plants and animals.
Moreover, they have higher implication in diagnosing and preventing various genetic disorders.
Mendel's Laws of Inheritance Citations:
- Mendel’s laws, Mendelian randomization and causal inference in observational data: substantive and nomenclatural issues. Eur J Epidemiol . 2020 Feb;35(2):99-111.
- Limits of imagination: the 150th Anniversary of Mendel’s Laws, and why Mendel failed to see the importance of his discovery for Darwin’s theory of evolution. Fly (Austin) . Jan-Mar 2013;7(1):28-38.
- Mendel’s law reveals fatal flaws in Bateman’s 1948 study of mating and fitness. Fly (Austin) . Jan-Mar 2013;7(1):28-38.
- ‘Rediscovery’ revised – the cooperation of Erich and Armin von Tschermak-Seysenegg in the context of the ‘rediscovery’ of Mendel’s laws in 1899-1901. Plant Biol (Stuttg) . 2011 Nov;13(6):835-41.
- Historical study: Johann Gregor Mendel 1822-1884. Am J Med Genet . 1991 Jul 1;40(1):1-25; discussion 26.
- A female contribution to early genetics: Tine Tammes and Mendel’s laws for continuous characters. J Hist Biol . Fall 1995;28(3):495-531.
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