(a) nonsynonymous; genetic drift (b) nonsynonymous; natural selection (c) synony
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(a) nonsynonymous; genetic drift (b) nonsynonymous; natural selection (c) synonymous; genetic drift (d) synonymous; natural selection 15. "Florida mice" essay question Describe Hopi Hoekstra's evidence for how coloration for Atlantic coast beach mice of Florida evolved independently from coloration for Gulf coast beach mice of Florida. Be specific in terms of the different genetic mechanisms associated with the formation of a similar phenotypic trait across the two beach mice populations. How did Hopi Hoekstra test the fitness (differential survival) associated with the presence or absence of the coloration trait in the beach mice? How do we know that the pale coloration trait of beach mice was derived from the ancestral coloration of mainland mice, and not vice versa? How could you test to see whether the change in coloration trait was heritable and not just a consequence of phenotypic plasticity? 16. "Introns and Exons" essay questionExplanation / Answer
Dr.Hopi Hoekstra and her colleagues have identified mutant alleles of pigment genes that produce blond coloration in beach mice. Blond mice suffer reduced predation by visual predators. With increased survival, blond beach mice are more likely to reproduce successfully and have higher evolutionary fitness than dark beach mice.
They found that Atlantic coast beach mice of Florida and Gulf coast beach mice of florida both evolved independently from mainland dark mice in order to achive survival fitness. The genetic mechanism involved is-1)a point mutation in the Mc1r (Melanocortin-1 receptor) gene altered the protein coded by that gene by one amino acid (Arg65Cys). Mc1r could no longer signal melanocytes to make eumelanin,moreover 2) A mutation in the regulatory region of the Agouti gene increased gene expression, producing more Agouti protein. Agouti binds to Mc1r on the melanocyte membrane and prevents signaling to trigger eumelanin production.
Hopi Hoekstra tested the fitness associated with presence or absence of the colouration trait in beach mice. They found that,dark mainland mice are camouflaged and less vulnerable to predation in a mainland grassy field habitat and Blond beach mice are camouflaged and less vulnerable to predation in a beach habitat.But if the beach mice are dark in colour,then they are more vulnerable to predation.
The pale coloration of beach mice was derived from ancestral coloration of mainland mice and not vice versa because the Arg65Cys mutation in Mc1r gene arose by chance, due to random substitution of one DNA nucleotide for another,it arose because beach mice needed blond coloration in order to be camouflaged in their new habitat,due to natural selection for blond coloration.Mc1r gene was not mutated in the ancestral population.
The change in coloration trait was heritable,not as a consequence of phenotypic plasticity because the change(mutation) was in the gene itself which was carried by the progenies generation after generation to maintain survival success and thus heritable.
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