Introduction

The beach mouse, (Peromyscus polionotus) is a small rodent found in southeastern United States. These mice are commonly found in old fields, but their ability to burrow better than most other species of mice also allows them to populate sandy beaches. There are several sub-species of these mice, each having a somewhat unique fur color, ranging from dark brown to very light brown, even approaching white.

The geography of fur colors is not random. The darkest colored subspecies tend to live inland while the lighter subspecies live on light sand beaches. This difference in fur color is due to genetic mutations that occurred, which in turn allowed natural selection to take place. One of the genes that was influenced to cause this fur color difference is the melanocortin-1-receptor, or MC1R. The following protein that the MC1R gene creates is responsible for producing the pigment found within fur. The pigment is what influences the color and shade of mouse fur. This case will examine the evolution of fur color in mice from the molecular level, involving MC1R and its mutations, along with the natural selection processes, and ultimately the evolution that occurred within these mice.