The Making of the Fittest:
Natural Selection and Adaptation
3. Which fur color seems to have the greatest overall selective advantage? Use data collected from both dark-colored and
light-colored substrates to support your answer.
6. According to the film, 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 collected 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.
Allele and Phenotype Frequencies in Rock Pocket Mouse Populations
HHMI
HOWARD HUGHES MEDICAL INSTITUTE
www.BioInteractive.org
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