[2 ] Constructional selection : When a gene exists in many duplicated copies, it may be maintained because of the many connections it has ( also termed pleiotropy ).
42.
Unfortunately, the process of antagonistic pleiotropy may result in an altered evolutionary path with delayed adaptation, in addition to effectively cutting the overall benefit of any alleles by roughly half.
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Pleiotropy occurs when one gene influences multiple, seemingly unrelated phenotypic traits, an example being phenylketonuria, which is a human disease that affects multiple systems but is caused by one gene defect.
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Pleiotropy not only affects humans, but also animals, such as chickens and laboratory house mice, where the laboratory house mice have found to exhibit the " mini-muscle " allele.
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The estimated heritability of schizophrenia is 70 % to 90 %, therefore the pleiotropy of genes is crucial since it causes an increased risk for certain psychotic disorders and can aid psychiatric diagnosis.
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The disposable soma theory and antagonistic pleiotropy theory are examples in which a compensating individual benefit, compatible with classical evolution theory ( See neo-Darwinism and modern evolutionary synthesis ) is proposed.
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An alternative theory is mTOR signaling is an example of antagonistic pleiotropy, and while high mTOR signaling is good during early life, it is maintained at an inappropriately high level in old age.
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This seems to be a direct hint that senescence arose because it conferred a direct evolutionary advantage, rather than some kind of side effect of genes that have other evolutionary advantages ( pleiotropy ).
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In a recent article, Carter and Nguyen identify several genetic disorders, arguing that far from being a rare phenomenon, antagonistic pleiotropy might be a fundamental mechanism for the survival of these non-optimal alleles.
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The protein products of the regulatory toolkit are reused not by duplication and modification, but by a complex mosaic of pleiotropy, being applied unchanged in many independent developmental processes, giving pattern to many dissimilar body structures.
