Standard 5a 1. What phenotypic variation (Vp) is present in this case study of beach mice? 2. What is the genetic origin of that variation? Be specific! 3. Evolutionary biologists believe that ancestral populations of beach mice likely had dark fur. As mice migrated to white sandy beaches, which color would likely have greater fitness? Briefly explain your reasoning. 4. Construct a model OR essay that explains how light coat color evolved in a population of beach mice that originally lacked this adaptation. Remember, your essay or model should include each of the key principles of natural selection we discussed in class (Vp, Vg, I, F, Eg, and Ep). In fact, circle or underline where these occur in your response.
I would like some help with question number two.
Context:
The beach mouse (Peromyscus polionotus) is a small rodent found in the southeastern United
States. Coat color in the beach mouse is variable, from dark brown to blonde (Figure 1). A pigment called eumelanin is responsible for some of the diversity in mouse coat color. The
MC1R gene, located on chromosome 8, plays a major role in the synthesis of eumelanin. There are two alleles of MC1R:
- R allele. Results in a functional MC1R protein that leads to stimulation of pigment production. This allele is found in dark colored mice.
- C allele. Results in a non-functional MC1R protein. Pigment production is, as a result, not stimulated. This allele is found in light colored mice.
Figure 1. Beach mouse with light fur (left) and dark (right).
These mice are hunted by visual predators like owls and fox. The distribution of coat color is not random. Beach mice with dark fur are found further inland, on dark brown soils while mice with light fur are found on beaches, where the sand is light brown. Dark fur mice also have to compete with another mouse species (Peromyscus maniculatus) that inhabits a similar ecological niche.
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