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Pleiotropy is a phenomenon that occurs when a single gene affects several characteristics of living creatures. Pleiotropy can be caused by a gene mutation. Marfan syndrome, a human genetic disease affecting the connective tissues, is an example of pleiotropy.
The eyes, heart, blood vessels, and bones are all often affected by this illness. Pleiotropy is produced by a mutation in a human gene that causes Marfan Syndrome.
What is Pleiotropy?
Pleiotropy is derived from the Greek pleio, which means “many,” and trepein, which means “influence.” Pleiotropy is the state of having numerous effects.
It is a term used in genetics to describe a single gene that controls or influences several (potentially unrelated) phenotypic characteristics. In pharmacology, it’s a characteristic of a medication that causes it to have extra (positive) effects in addition to the ones it was designed to have.
It is demonstrated in molecular biology by cyclic AMP in a cell, which has a range of effects via controlling a protein kinase, which impacts a variety of other proteins.
Is Cystic Fibrosis an Example of Pleiotropy?
One of the most frequent examples of pleiotropy is cystic fibrosis, which is a hereditary disease. Lung infections are common with this condition. The digestive system and other organs in the body might be affected by this condition. Cystic fibrosis is caused by a mutation in the “cystic fibrosis transmembrane conductance regulator gene,” which prevents the gene from functioning properly.
Is Albinism a Pleiotropy?
Albinism is caused by a pleiotropic gene produced by a tyrosinase (TYR) gene mutation. The afflicted person’s body produces less melanin as a result of the mutation.
Pleiotropic genes are genes that influence the behaviour and functions of several genes with unrelated characteristics. On occasion, such qualities have been seen to be extremely similar in nature, while in other situations, they have been noted to be very unlike.
Pleiotropic characteristics are a term used to describe the issues caused by pleiotropic genes.
Effect of Genes on Traits of Humans
The phenotype refers to the physical characteristics of a person, such as body shape, height, colour, physique, and height. A trait governed or controlled by a single gene is known as a single gene trait. It may be difficult to determine the presence of pleiotropic characteristics until the gene is subjected to mutation.
Mutations are alterations in DNA sequences that occur relative to one another. The point mutation is the most frequent form of gene mutation, which is further divided into silent mutations, nonsense mutations, and missense mutations.
The character of the qualities is generally determined by the two alleles, which are the variation forms of a gene, according to diverse publications. The combinations of particular alleles dictate the synthesis of proteins that derive the process of phenotypic trait development, whilst the DNA sequence of the gene is altered by the mutation that occurs in the gene.
As a result, alterations in the gene segment sequences cause the proteins to stop working. As a result, the progression in the mutation will affect all accessible characteristics that are connected to a single attribute in the pleiotropy process.
Pleiotropy in Genetics
Pleiotropy was first proposed in biology by Gregor Mendel, a well-known geneticist well known for his groundbreaking work on pea plants. He tried purple-flowered plants and white-flowered plants in a series of trials.
Colorful blooms and leaf axils are always visible on plants with coloured seed coats, he observed. An axis is the portion of the plant that connects the stems to the rest of the plant.
He noticed that, although the seed coats were colourless in nature and had no colour in their axis, the pea plants, which were the focus of the study, invariably had white blooms.
After reviewing his findings, it was determined that the colour of the plant’s axil and the seat coat are the most crucial elements in determining whether the plant would produce white or purple flowers. Today, similar findings are attributed to the phenomenon of pleiotropy, in which a single gene contributes to numerous phenotypic characteristics.
Pleiotropy may be caused by a number of different processes, including development pleiotropy, gene pleiotropy, and selectional pleiotropy.
The focus of gene pleiotropy is on the functionality of a specific gene, and this type of pleiotropy is also known as molecular gene pleiotropy. The functions of a characteristic are generally determined by the number of traits and biochemical components influenced by the gene.
The biochemical parameters include the number of enzyme reactions performed by the gene’s protein products. In the evolution of pleiotropy, the major focus is on mutations and their relative influence on a variety of characteristics. It has been shown that single-gene alterations have a broader influence on numerous other potential characteristics.
Furthermore, illnesses involving mutational pleiotropy are defined by deficits in many organs that disrupt the proper functioning of multiple bodily systems. The last process that causes pleiotropy is selectional pleiotropy, which focuses on the impact of gene mutations on the number of distinct fitness components.
The method by which an organism transmits its genes from one generation to the next through sexual reproduction is typically governed by the fitness of the organism. Selectional pleiotropy is frequently concerned with the effects of selection on naturally occurring characteristics.
Polygenic vs Pleiotropy
Many people confuse the meanings of polygenic inheritance with pleiotropy, which is a common finding. The main difference between the two is that pleiotropy occurs when a single gene influences several traits, whereas polygenic inheritance occurs when a single trait is regulated by many distinct genes, such as skin colour.
Pleiotropy vs Epistasis
Understanding the idea and meaning of epistasis, as well as its relationship to pleiotropy, is also critical.
Epistasis refers to the interplay of several genes in influencing phenotypic results.
Pleiotropic gene research is important in biology because it helps researchers understand how specific genes are frequently implicated in genetic diseases. Pleiotropy may be found in abundance throughout nature.
Pleiotropic disorders include fruit flies with vestigial genes, poultry with frizzle characteristics, the process of pigmentation and deafness in cats, pleiotropic sickle cell diseases in humans, and phenylketonuria (commonly known as PKU).
Pleiotropy is influenced by both direct and indirect pleiotropy, as evidenced by instances found in numerous literature research.
For example, if a blind mouse is born as a result of changes in a single gene, the odds are quite high that the blind born mouse will struggle with visual learning tests, showing that a single gene is implicated in many pathways.
As a result, there are numerous examples of both direct and indirect pleiotropy, some of which are discussed in further detail in the sections below.
i. The Vestigial Gene and Fruit Flies
Vestigial genes are important in the development of the wing of the fruit fly Drosophila. If these flies are homozygous for the recessive version of the vestigial gene, they have small wings and are unable to fly in the proper manner (VG). As a result, the vestigial gene is pleiotropic, resulting in the fruit fly drosophila’s wings not developing.
Other indirect impacts of pleiotropy in fruit flies include a reduction in the number of eggs present in the ovaries of the flies, a shift in the location of the bristles on the scutellum of the flies, and a shorter life span of the flies. The wings of the first bee are not entirely formed, as opposed to the fully developed wings of the second bee.
ii. Deafness and Pigmentation in Cats
Deafness is present in around 40% of cats with white hair and blue eyes, according to reports. Although this information is intriguing because we have most likely never paid attention to these cats throughout our lives.
It was discovered early on in the research that white cats with one blue eye and one yellow eye were blind in one eye, which was typically the blue eye, but it was subsequently shown that this occurrence of blindness does not necessarily apply to all cat breeds.
Waardenburg syndrome is a human disease that is comparable. Pleiotropic genes are involved in this disease in cats, producing not just deafness but also colouring issues. The goal of the study was to figure out how hearing capacity and the pigmentation process are linked.
Pigmentation has a critical function in regulating fluid flow in the ear canals, according to the findings, which were conducted on mice. Those who lacked pigmentation also lacked the flow of fluids through the ear canals, causing them to rupture and eventually lead to deafness.
iii. Frizzle Traits of Chickens
Pleiotropic genes cause the hens to express a variety of genes. Walter Landauer and Elizabeth Upham discovered in 1963 that hens with the dominant frizzle gene generate feathers that curl all over their bodies rather than laying flat against their skin.
This impact was linked to the genes’ phenotypic effects. Furthermore, it was discovered that these frizzle characteristics induced a variety of alterations in the hens, including aberrant body temperatures, high blood flow rates, high metabolic rates, and increased digestive capacity.
Furthermore, as compared to typical wild eggs, the hens with pleiotropic characteristics produced fewer eggs, affecting their reproduction rates.
iv. Marfan Syndrome
The Marfan syndrome is a hereditary disease that causes problems with tissue connections. The eyes, heart, bones, and blood arteries are the most commonly affected parts of this condition. People who suffer from these disorders generally have long, slender bodies with long legs, arms, fingers, and toes, and the Marfan syndrome can cause mild to severe damage.
The symptoms of the condition differ from one family to the next, and they also differ by age, with some experiencing minor symptoms and others experiencing life-threatening problems. Cardiovascular problems include aortic aneurysms, aortic dissections, and valve abnormalities.
Eye difficulties, such as lens dislocations, retinal issues, and early-onset glaucoma, commonly known as cataracts, are, on the other hand, extremely essential.
v. Sickle Cell Disease
The most frequent kind of pleiotropy that affects humans is sickle cell disease, which is caused by a condition that causes irregularly shaped red blood cells, whereas normal red blood cells have a biconcave, disc-like shape and contain large amounts of haemoglobin.
Red blood cells in the blood are primarily responsible for binding tissues and transporting oxygen to all accessible cells. Sickle cells are most commonly caused by mutations in the beta-globin gene. As a result, irregularly shaped blood cells cluster together, creating a block in the veins and eventually stopping blood flow in the veins.
This obstruction causes a slew of health issues as well as harm to critical human organs, including the heart, brain, and lungs.
Phenylketonuria, or PKU, is another frequent type of pleiotropy, which causes mental impairment, hair loss, and changes in skin colour or pigmentation. The majority of these illnesses are caused by a significant number of mutations in a single gene on a chromosome.
These genes are involved in the synthesis of phenylalanine hydroxylase enzymes. These enzymes are responsible for breaking down the amino acid phenylalanine, which we obtain via protein digestion. Pleiotropy causes the nervous system to be harmed when the amount of amino acids rises owing to pleiotropy.
Other diseases induced by phenylketonuria include intellectual impairments, cardiac issues, developmental delays, and seizures. Classic PKU is the most prevalent kind of PKU, and it usually affects infants. The prevalence of these disorders varies depending on where you live.
In the United States, one out of every ten thousand newborns is affected by this illness. The good news is that doctors can diagnose PKU in newborns based on their early symptoms, allowing them to begin therapy early and save the youngsters from the disease’s devastating consequences.
Antagonistic pleiotropy is a theory offered to explain senescence or biological ageing that can be ascribed to natural selection of specific pleiotropic genes.
Natural selection may prefer an allele that has a detrimental influence on the organism if it also provides beneficial aspects of antagonistic pleiotropy. Furthermore, natural selection favours genotypes that improve reproductive fitness early in life but induce biological ageing later in life.
The sickle cell, where the Hb-S allele mutation of the haemoglobin gene gives varied advantages and drawbacks for their survival, is the most typical example of antagonistic pleiotropy.
The homozygous for the Hb-S allele, which has a couple of Hb-S alleles of the haemoglobin allele, has a shorter lifespan due to the negative effects of sickle cell traits, whereas the heterozygous traits, which usually have one normal allele and a single Hb-S allele, are highly resistant to malaria and do not have the same negative symptoms.
Furthermore, it may be deduced that the frequency of the Hb-S allele is higher in geographical areas with higher malaria transmission rates. Lethal alleles are those that result in the death of the individual who has them.
Generally, they are the result of gene mutations that are highly important for an individual’s development and growth. A dominant, recessive, or codominant allele can exist. An individual with the AB blood type possesses both alleles, i.e. allele A and allele B. This is an example of a codominant allele.
Pleiotropy is a characteristic that demonstrates that several genes have many phenotypic effects, which may be summarised from the preceding explanation. Pleiotropy may be caused by a number of different processes, including development pleiotropy, gene pleiotropy, and selectional pleiotropy.
The focus of gene pleiotropy is on the gene’s functionality, whereas the focus of development and selectional pleiotropy is on mutations and their relative influence on numerous characteristics, and the effect of gene mutations on the number of distinct fitness components, respectively.
Pleiotropic gene research is important in biology because it helps researchers understand how particular genes are involved in a variety of genetic disorders. Pleiotropy is implicated in a number of genetic diseases that have been reported in the literature.
Deafness and pigmentation in cats, the prevalence of frizzle features in cats, Marfan syndrome in humans, sickle cell disease, phenylketonuria (PKU), albinism, Austin, and schizophrenia are only a few examples of pleiotropic qualities.
- Evaluating the potential role of pleiotropy in Mendelian randomization studies. Hum Mol Genet . 2018 Aug 1;27(R2):R195-R208.
- Pleiotropy and Specificity: Insights from the Interleukin 6 Family of Cytokines. Immunity . 2019 Apr 16;50(4):812-831.
- What Is Antagonistic Pleiotropy? Biochemistry (Mosc) . 2019 Dec;84(12):1458-1468.