Dr. Nachman and his colleagues collected rock pocket mice across 35 kilometers of the Arizona Sonoran Desert, which included both dark, rocky lava outcrops and light, rocky, granite areas. They recorded substrate color, and coat-color frequencies for each location. Each site was separated from any of the others by at least eight kilometers. The researchers trapped a total of 275 mice. Their data are summarized below (numbers have been slightly modified for the purposes of this worksheet). (numbers have been slightly modified for the purposes of this worksheet).
Field Data Summary
Collecting Site Substrate Color Number of Mice Phenotype
Light Dark
1 Dark 22 3 19
2 Light 80 74 6
3 Light 22 19 3
4 Dark 28 3 25
5 Light 58 25 33
6 Dark 65 9 56
1. Calculate the overall frequencies of light-colored mice and dark-colored mice caught on light-colored substrates.
2. Calculate the overall frequencies of light-colored mice and dark-colored mice caught on dark-colored substrates.
3.Using the Hardy-Weinberg equation and data from the table above, determine the frequency of the three genotypes on the light, rocky, granite substrate.
4. Using the Hardy-Weinberg equation and data from the table above, determine the frequency of the three genotypes on the dark, rocky lava substrate.
5. Which fur color seems to have the greatest overall selective advantage?
6.What environmental change gave a selective advantage for one coat color over another?
7. In a separate study, 76 rock pocket mice were collected from four different, widely separated areas of dark lava rock. One collecting site was in Arizona. The other three were in New Mexico. Dr. Nachman and colleagues observed no significant differences in the color of the rocks in the four locations sampled. However, the dark-colored mice from the three New Mexico locations were slightly darker than the dark-colored mice from the Arizona population. The entire Mc1r gene was sequenced in all 76 of the mice collected. The mutations responsible for the dark fur color in the Arizona mice were absent from the three different populations of New Mexico mice. No Mc1r mutations were associated with dark fur color in the New Mexico populations. These findings suggest that adaptive dark coloration has occurred at least twice in the rock pocket mouse and that these similar phenotypic changes have different genetic bases. How does this study support the concept that natural selection is not random?
8. To determine if the rock pocket mouse population is evolving, explain why it is necessary to collect fur color frequency data over a period of many years.