Pleiotropy - Definition and examples - Online biology dictionary (2023)

Definition of pleiotropy

as a bachelorGenbegins to affect several characteristics of living organisms, this phenomenon is known asPleiotropie. AMutationin a gene can lead to pleiotropy. An example of pleiotropy isMarfan Syndrome, a human genetic disease that affects theconnective tissue. This disease commonly affects the eyes, heart, blood vessels, and skeleton. Marfan syndrome is caused by a mutation in a human gene that leads to pleiotropy.

Pleiotropy (definition of biology):the condition of having multiple effects. InGenetic,refers to an individualGenControlling or influencing multiple (and possibly unrelated) phenotypic traits. InPharmacology,can be a property of a drug in which it (advantageous) in addition to the purpose for which it was intended. Inmolecular biology, exemplified by thecyclic AMPin a cell where it produces a variety of effects as it controls a protein kinase which in turn affects several other proteins.Etymology:from the Greek pleio, meaning "many" and
trepein, meaning "to influence."

Is cystic fibrosis an example of pleiotropia?

cystic fibrosisIt is a genetic disorder and one of the most common examples of pleiotropy. In this disorder, lung infections are persistent. This disease can also affect thedigestive systemand other organs of the body. The mutation in the cystic fibrosis transmembrane conductance regulator gene disrupts the proper functioning of this gene, resulting in cystic fibrosis.

Is albinism a pleiotropia?

Sim,albinismit is also due to a pleiotropic gene caused by a mutation in the tyrosinase gene (TYR). The mutation changes the production ofMelaninin the body of the person concerned.

The genes that control the behavior and functionality of multiple genes that share unrelated traits are referred to aspleiotrope Gene. It has sometimes been observed that these characters are very similar in nature, while on many occasions they tend to be very dissimilar to one another. Problems that arise due to pleiotropic genes are sometimes referred to aspleiotropic properties. (See Figure 1)

How does a gene affect a person's characteristics?

Physically expressed characteristics such as body shape, height, color, build and height are referred to asphenotype. A single gene trait can be defined as a trait that is determined or controlled by a particular gene. It can be difficult to detect the presence of pleiotropic traits unless the mutational process occurs in the gene.

The relative changes that occur in the sequences of theDNSare called mutations. The most common type ofGen Mutationand thePoint mutationwhich is still classifiedsilent mutations,meaningless mutations, zmeaningless mutations. (Learn more aboutgenetic mutations: BuchGenetic mutations tutorial)

It has been observed in various literatures that the twoAlleles, which are the variant form of a gene, usually determine the type of traits. The production of proteins resulting from the process of phenotypic trait development is determined by combinations of the specific allele while the DNA sequence of the gene is altered by the mutation occurring in the gene. So, the nonfunctioning of the proteins is the result of changes in the sequences of the gene sections. Therefore, in the process of pleiotropy, all available traits associated with a single trait are altered by mutational progressions.

Pleiotropy in Genetics

The idea of ​​pleiotropy in biology was given by a famous geneticist,Gregor Mendel, which is known in history for its remarkable achievements in pea plants. He conducted a series of experiments with purple-flowered and white-flowered plants. He noted that the colored flowers and colored leaf axils are always exhibited by plants with colored involutes. The parts of the plant that connect to the stems are called the axis.

He testified that specifically the pea plants that were the focus of the research always had white flowers, although the seed coats were naturally colorless with no pigmentation on their axis. After summarizing his research, it was concluded that the color of the plant's axils and the mantle of the seat are the important factors that determine the color of whether the plant will show white or purple flowers. Therefore, today these observations have been considered due to the result in pleiotropyA single gene contributes to multiple phenotypic traits.

Often pleiotropy can arise due to very overlapping but distinct mechanisms, such as:development of pleiotropy,genetic Pleiotropy, zselektive Pleiotropie.

Emgenetic Pleiotropythe focus is on the functionality of the respective gene and this form of pleiotropy is also referred to as molecular gene pleiotropy. The number of traits and the biochemical factors influenced by the gene often determine the functions of a particular trait. The number of enzymatic reactions catalyzed by the protein products of the gene is included in the biochemical factors.

The main focus in the development of pleiotropy is on mutations and their relative effects on many traits. It can be seen that single gene mutations usually have broader implications, altering several other possible traits. In addition, diseases associated with mutational pleiotropia are categorized according to deficiencies in the various organs that affect the proper functioning of many body systems.

The final mechanism leading to pleiotropy is invokedselektive Pleiotropie, which focuses on the impact of genetic mutations on the number of individual fitness components. The process by which each organism transfers its genes from its generation to the next generation through sexual reproduction is usually determined by its level of fitness. Selective pleiotropy often deals with the effects of selection on natural traits.

Poligenico against pleiotropy

It is a very common observation that many people confuse the meaningPolygenic inheritancewith pleiotropy. The main reason that differentiates them is that when a single gene affects multiple traits, it is termed pleiotropy, while it falls under the definition of polygenic inheritance when a single trait is controlled by many of the multiple genes, such as: B. Skin pigmentation.

Pleiotropie x Epistasia

Another important thing is to understand the concept and meaning ofEpistasisand its relation to pleiotropy. The interaction of multiple genes in determining phenotypic outcomes is called epistasis. (Ref.1)

The study of the pleiotropic gene is of great importance in biology as it helps to understand how often certain genes are involved in some of thegenetic disorders.

There are many examples of pleiotropy that are easy to find in nature. Fruit flies and the residual gene, chickens and their frizzy traits, the pigmentation process and deafness in cats, sickle cell pleiotropy in humans, and phenylketonuria (also spelled PKU) are some of the most common examples of pleiotropic conditions. They are detailed below.

Examples of pleiotropy

The examples of pleiotropy found in several studies in the literature are due to the influence of direct and indirect pleiotropy. For example, you can take the example of a mouse that was born blind due to changes in a single gene, and in these examples the chances are very high that the mouse born blind is very bad at learning visual tasks, confirming that a single gene will be involved in multiple pathways. Hence, there are many examples of direct and indirect pleiotropy, some of which are discussed in more detail in the following sections.

The residual gene and fruit flies

Residual genes play a very important role in wing developmentDrosophila, that's a fruit fly. They develop short wings and cannot fly properly when these flies are homozygous for the recessive form of the flyGen Rest(VG). Thus, the residual gene is pleiotropic, resulting in a lack of wing development in the Drosophila fruit fly. Furthermore, reducing the number of eggs present in the ovaries of the flies, changing the bristle positions on the scutellum of the flies, and reducing the time of the flies' life cycle are some other indirect effects of pleiotropy in the fruit fly. The elaboration of the pleiotropy is in Fig. 2. It can be seen that the wings of the first bee are not fully developed compared with the second bee which has fully developed wings. (ref 2)

Deafness and pigmentation in cats

It has been reported that about forty percent of white-coated, blue-eyed cats are deaf (Figure 3). While this fact is quite intriguing, we probably haven't paid any attention to these cats in our entire lives. In the early stages of research, it was observed that white cats that have one blue eye and one yellow eye were blind in one eye and that it was mainly the blue eye, but later it turned out that this blindness phenomenon is not always valid is for all cat breeds. In humans is a similar disorderSindrome de Waardenburg.

In cats, this condition involves pleiotropic genes that not only cause deafness but also affect pigmentation. The researchers tried to understand how hearing ability and the pigmentation process are related. The experiments were conducted on mice and revealed that pigmentation plays a very important role in maintaining fluid flow in the ear canals. Those with a lack of pigmentation also lack fluid flow in the ear canals, leading to theirdemolition, and finally to deafness. (ref 3)

Frilled traits in chickens

There are several genes displayed by chickens as a result of pleiotropic genes. It was observed in 1963 by Walter Landauer and Elizabeth Upham that chickens that diekrause GeneThey mostly produce feathers that curl around their entire body instead of lying flat against the skin. This effect was related to the phenotypic effects of the genes. In addition, these frizzy traits have been observed to cause many changes in chickens, the most notable being abnormal body temperatures, high blood flow rates, high metabolic rates and increased digestive capacity. Additionally, hens with pleiotropic traits laid fewer eggs compared to normal wild eggs, affecting their reproductive rates. The presence of the ruffled features of the chicken can be seen in the video below.

Marfan Syndrome

The inherited condition that causes tissue connectivity problems is called Marfan syndrome. This type of syndrome mainly affects the eyes, heart, skeleton and blood vessels. People suffering from these syndromes usually have long and thin bodies with long legs, arms, fingers and toes, while Marfan syndrome can cause mild or severe damage. Symptoms of the syndrome can vary from one family to another and it also depends on age, with some experiencing very minor symptoms and many experiencing life-threatening complications. Aortic aneurysms, aortic dissection and valvular malformations are consequences of cardiovascular complications. On the other hand, eye complications, lens displacements, retinal problems and early onset glaucoma, also known as cataracts, are very important. (ref 4)

Sickle cell anemia

The very common examples of pleiotropia that usually occurs in humans is called sickle cell disease, which occurs due to the developed disorder of irregularly shaped red blood cells, while normal red blood cells have a biconcave, disk-like shape and large amounts of hemoglobin are found.

How is sickle cell anemia an example of pleiotropia?

The main job of the red blood cells in the blood is to connect tissues and carry oxygen to all available cells. Mutations in the beta globin gene usually lead to the formation of sickle cells. This causes the irregularly shaped blood cells to clump together, forming a blockage in the veins and eventually blocking the flow of blood in the veins. This blockage leads to many health problems and causes damage to many vital human organs such as the heart, brain and lungs. The comparison between normal red blood cells and sickle cells is shown in Figure 5. (ref 5)

Phenylketonuria or PKU

Another common example of pleiotropia is phenylketonuria, or PKU, which causes mental retardation, hair loss, and changes in skin color or pigmentation. These diseases usually occur as a large number of mutations in a single gene on a chromosome. These genes are responsible for the production of enzymes known asPhenylalaninhydroxylase. These enzymes normally break down amino acidsPhenylalaninwhich we get by digesting proteins. When amino acid levels increase due to pleiotropy, it leads to damage to the nervous system.

Mental retardation, heart problems, developmental delays, and seizures are some of the other disorders caused by phenylketonuria. The most common PKU is calledclassic PKU, which usually affects newborns. The incidence of these diseases varies from place to place. In the United States in particular, one in ten thousand births suffers from this disease. The good thing, however, is that doctors can identify PKU in babies based on their early symptoms, allowing the doctor to start treatments early and save children from the serious effects of this disease.

Antagonistic Pleiotropy

A proposed theory to explain senescence, or biological aging, which can be attributed to natural selection of certain pleiotropic alleles is presentedAntagonistic Pleiotropy. An allele that may adversely affect the organism may be favored in natural selection if the allele also produces beneficial factors in antagonistic pleiotropy. In addition, natural selection typically selects for alleles that increase reproductive capacity early in life but promote biological aging later in life.

The most common example of antagonistic pleiotropy is sickle cells, in which mutation of the Hb S allele of the hemoglobin gene offers several advantages and disadvantages for their survival. Homozygotes for the Hb S allele, who have a pair of Hb S alleles from the hemoglobin allele, have relatively shorter lifespans due to the negative effects of sickle cell traits, while heterozygotes, who normally carry a normal allele and a single O Hb S have alleles are highly resistant to malaria and do not show the same degree of negative symptoms. In addition, it can be concluded that the frequency of the Hb S allele is higher in geographic locations with higher malaria transmission rates.

Alleles that cause the death of the person carrying them are called lethal alleles. They are usually the result of genetic mutations that are extremely important for the development and growth of individuals. An allele can be dominant, recessive, or codominant. Aco-dominantAn example of an allele is a person with aABBlood group in which the person has both alleles, i.e.Tongue AeAllelo B.

Summary

To summarize from the discussion above, the trait of having multiple genes have many phenotypic effects is called pleiotropy. Pleiotropy can usually arise through some of the very overlapping but distinct mechanisms, such as: B. Developmental pleiotropy, gene pleiotropy and selective pleiotropy. Gene pleiotropy focuses on the functionality of the particular gene, while developmental and selective pleiotropy focuses on mutations and their relative impact on many traits, or the impact of gene mutations on the number of individual fitness components. The study of the pleiotropy gene is of great importance in biology as it helps to understand how certain genes are often involved in some genetic diseases, as many genetic diseases caused by pleiotropy are cited in the literature. Deafness and pigmentation in cats, presence of frizzy facial features in cats, Marfan syndrome in humans, sickle cell anemia, phenylketonuria or PKU, albinism, Austin and schizophrenia are some of the many examples of pleiotropics.

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