PLEIOTROPY- MEANING, CLASSES & EVOLUTION
Introduction
Pleiotropy refers to the phenomenon of a single gene affecting multiple traits. The word “Pleiotropy” is derived from Greek pleion, means “more”, and tropos, means “way” and occurs when one gene affects two or more characters.
Pleiotropic gene– Gene that exhibits multiple traits.
Classes (Arise of Pleiotropy)
Pleitropy entail a mapping from one thing at the genetic level to multiple things at a phenotypic level. The natures of the things vary in different contexts. Pleiotropy can arise from several distinct but potentially overlapping mechanisms, such as gene pleiotropy, developmental pleiotropy, and selectional pleiotropy.
- Gene pleiotropy
This concept implies the number of functions a molecular gene has. These functions can be defined either genetically through the number of measured characters affected by a knockout, or biochemically, for example, by the number of protein-protein interactors a gene has or the number of reactions it catalyzes. Gene pleiotropy occurs when a gene product interacts with multiple other proteins or catalyzes multiple reactions.
- Developmental pleiotropy
Here mutations are relevant unit but not molecular gene. Developmental pleiotropy is a feature of the genotype-phenotype map that defines the genetic and evolutionary autonomy aspects of phenotype, independent of fitness. Simply, it occurs when mutations have multiple effects on the resulting phenotype.
- Selectional pleiotropy
Here the question is about the number of separate components of fitness a mutation affects. Selectional pleiotropy occurs, when the resulting phenotype has many effects on fitness based on factors such as age and gender. A key feature of selectional pleiotropy is that traits are defined by the action of selection and not by the inherent attributes of the organism.
Pleiotropy and Evolution
Pleiotropy can have an effect on the evolutionary rate of genes and allele frequencies.
In the context of life history evolution, pleiotropy means that a single gene affects the fitness of the organism at two or more ages. If a new mutation improves fitness in both young and old animals, then it is likely to be favored by natural selection, and will increase in the population.
Conversely, a gene that decreases fitness in both young and old organisms will be eliminated by natural selection. The more interesting cases are those in which the fitness effects on young and old organisms are negatively correlated, a condition referred to as ‘negative pleiotropy’ or ‘antagonistic pleiotropy.’ Medawar’s principle suggests that mutations that improve early fitness at the expense of late fitness will be favored by natural selection, while those with the converse effects will be eliminated.
As far as human molecular genetics concerned, Pleiotropy refers to disorders where multiple, seemingly unrelated organ systems are affected.
For example, one individual in a pedigree may exhibit cardiac arrhythmia, whereas another individual with the same disorder in either the same or different pedigree shows muscle weakness and deafness. Since the manifestations of disease are so vastly and usually inexplicably different, disorders that show a high degree of pleiotropy are often difficult to diagnose. As a group, mitochondrial disorders typically show a high degree of pleiotropy, as any organ system can be affected, to almost any degree, with any age of onset.
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