Population Genetics

Since the populations of mice were separated over generations ago, these populations were isolated from each other. Once they were isolated, these populations were then subject to their own natural selection. Depending on the type of environment each mouse population called their home, they each underwent specific natural selection, each of which favored their survival within their surroundings. 

What does this mean? Well, mouse populations present on light, sandy beaches were more likely to survive if they had lighter fur, and could blend into their surroundings better. Same with populations present on darker, dirt lands; mice with darker fur would have a higher chance of survival. Since mouse predators, such as owls and foxes, are sight predators, mice have a better chance of surviving if they match their environment. 

This selection pressure allows for the phenotype of the mouse fur color to shift towards what is more favorable. This occurs when the genotype of the mouse population changes in frequency. The MC1R gene, for example, had a higher chance of developing a mutation on alleles within mice populations that inhabited the light sandy beaches. However, it’s also more likely that the MC1R gene would retain its normal phenotype when inhabiting darker, forest environments. Within this visual, the numerous isolated populations each have a different frequency for each allele; some having only the R allele (which codes for eumelanin production) or some having both the R allele and the C allele (the cysteine substitution, which inhibits eumelanin production).