Question

(Answer in no more than 400 words) Explain what Additive Genetic Covariance refers to. Explain how Additive Genetic Covariance plays a role in: 1) the evolution of senescence, 2) runaway sexual selection, and 3) a trait evolving in the opposite direction from where selection is pushing it.

Answer 1

Answer-

Additive genetic covariance-The additive genetic covariance include genetic variations individuals (due to individual’s carrying different alleles), and can be used to predict phenotypic responses to directional selection. But additive genetic covariance, itself is subject to evolution, and by comparing the additive genetic covariance among naturally or experimentally evolving taxa we can understand how selection and drift produce changes in frequencies of alleles that determine phenotypes.

Role of Additive genetic covariance-

1-The evolution of senescence- various scientist suggested that genetic variance components differ under the two mechanisms of senescence, under mutation accumulation additive covariance, dominance variance, homozygote variance and inbreeding depression should all increase with age. By contrast, working with the assumption that antagonistic pleiotropy loci are overdominant (i.e. that they contribute to segregating genetic variation by heterozygote advantage), under antagonistic pleiotropy, only additive variance is expected to increase with age.

2-Runaway sexual selection- Fisher’s model explains the origin of sexual preference for particular male traits, and the runaway selection phase during which the male characteristic may lose its additive genetic variance. Cases in which the additive genetic variance in the male trait is lost, females selecting males with exaggerated traits would no longer increase the probability that their sons would have exaggerated traits, but would still pay the costs for selecting extreme males. During the course of evolution from some slight expression of a
characteristic to its “runaway” exaggerated form, the additive genetic variance might be severely low many times to be slowly overcome by new mutations. During these periods of very low additive genetic variance, the handicap principle could account for the maintenance of female preference for extreme forms.

3-Opposite responses of traits to the selection- Using different genetic models like additive genetic covariance for the response to selection, we can see when opposite responses to selection should be expected. These typically occur when social selection opposes direct selection, when individuals interact with others less related to them than a random member of the population, and if the genetic covariance between direct and indirect effects is negative. We can conclude the likelihood of each of these occurring in nature and therefore summarize how opposite responses to selection are likely to be!