From Darwin to DNA: The Genetic Basis of Color Adaptations by Hopi Hoekstra ( Ar

Question

From Darwin to DNA: The Genetic Basis of Color Adaptations by Hopi Hoekstra ( Article Link: https://nescent.org/media/NABT2010/pdf/Hoekstra.pdf) What is the role of Mc1r in determining pigmentation? What is the prediction for Mc1r activity in beach mice? Why is Figure 6 C the accepted cladogram including multiple origins of light color? Is the mechanism (gene mutation) leading to light fur color the same for the Gulf and Atlantic coast species? What point was the author making when discussing wooly mammoths, fence lizards and the snow goose (Figure 7)? What did you find most interesting about the article? Answer those question, please.

Explanation / Answer

The Mc1r receptor is associated with melanocytes, the pigment-producing cells. Mc1r acts as a switch in determining the type of pigment a melanocyte produces either eumelanin (brown to black pigment) or phaeomelanin (blonde to red pigment). When Mc1r is “turned on,” it signals through a cascade of effects in the melanocyte cell for dark eumelanin to be produced; when Mc1r is “turned off” and signaling is reduced, the default state is restored and light phaeomelanin is produced.

Single mutation at nucleotide position 293, which codes for Mc1r protein, is one of difference present between the DNA of mainland and beach mice where beach mice have thymine (T) and mainland mice have a cytosine (C). The C-to-T mutation is unique to light-colored beach mice. This single nucleotide mutation causes an amino acid change in the protein. Cysteine (small uncharged) is present in the place of Arginine (large charged) at amino acid position 65. This radical change in the Mc1r protein’s chemistry is predicted to affect the structure of the protein, shows decreased activity and therefore lower signaling, leading to light pigmentation.

Using DNA to trace the ancestry of populations, the five pale Gulf Coast subspecies are found to be very closely related and they are more genetically similar to the dark mainland mice from Florida’s panhandle than to the pale Atlantic beach mice. Similarly, Atlantic coast beach mice are most similar to mainland mice from central Florida. These data suggest that light coloration has evolved independently on the Gulf and Atlantic coasts. Hence, the cladogram with multiple origins of light color is accepted.

No, the Mc1r - Arg65Cys mutation does not contribute to light pigmentation on the Atlantic coast species.

Mutations in Mc1r contribute to color variation in several vertebrate species. The same mutation that occurs in beach mice is also found in a population of mammoths
suggesting they, too, may be variable in color. Different mutations in Mc1r contribute to similar color differences in lizards and birds. Based on these data, the author suggests that mammoths, lizards, snow goose and mice all evolved the exact same mutation.

The various genetic solutions that are seen within a single species to a common ecological problem of blending into the local environment, which in turn has a large effect on the fitness of the species in the wild is the most interesting feature in this article.

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