Question

Explain and contrast two explanations for the evolution of senescence: Antagonistic Pleiotropy Theory and Mutation/Selection Balance Theory.

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Answer 1

Antagonistic pleiotropy: If selection cannot counteract the deleterious effects on old age then we can say that mutations or alleles with opposite pleiotropic effects exist at different ages i.e, genetic variants exhibit beneficial effects on fitness early in life when selection is strong, but have deleterious effects late in life when selection is weak. Alleles of the gene increase some components of fitness at a cost inorder to balance selection, and maintain genetic variation in fitness traits.

Mutation selection : If the effects of deleterious mutation is restricted to late ages then effect of this mutation is already passed on to the next generation before the negative late-life effects become apparent. In such situations, natural selection is weak and inefficient to eliminate such mutation and also neutral mutations accumulate in the population by genetic drift as evolution occurs which lead to the evolution of aging.