The rock pocket mouse, Chaetodipus intermedius, is a small, nocturnal animal found in the deserts of the southwestern United States. Most rock pocket mice have a sandy, light-colored coat that enables them to blend in with the light color of the desert rocks and sand on which they live. However, populations of primarily darkcolored rock pocket mice have been found living in areas where the ground is covered in a dark rock called basalt caused by geologic lava flows thousands of years ago. Scientists have collected data from a population of primarily dark-colored mice living in an area of basalt called the Pinacate lava flow in Arizona, as well as from a nearby light-colored population. Researchers analyzed the data from these two populations in search of the genetic mutation responsible for the dark coat color. Their analyses led to the discovery of a mutation in the Mc1r gene that is involved in coat-color determination. 

After you watch the video above, read the information below to learn more about the genetic mutations in the rock pocket mouse MC1R gene.

Two pigments primarily determine the coat color of rock pocket mice: eumelanin, which is dark-colored, and pheomelanin, which is light-colored. The products of several genes, including the Mc1r gene, control the synthesis of these pigments. This gene encodes a protein called the melanocortin 1 receptor (MC1R) and is found embedded in the cell membranes of melanocytes, specialized pigment-producing skin cells. The melanocytes of wild-type (nonmutant) mice produce more pheomelanin than eumelanin. The result is a sandycolored mouse. The mutated version of the Mc1r gene, however, triggers melanocytes to increase the production of eumelanin, resulting in the dark coat-color phenotype.

A gene mutation is any change in the DNA sequence of a gene. Gene mutations can change the structure of the resulting protein. A change in protein structure can change, negate, or have no effect on function. There are several types of mutations, and they affect the amino acid sequences of proteins in different ways. Types of mutations: 

Using the DNA nucleotide sequences for the wild-type and mutant genes in the following tables (page 3), determine the complementary mRNA sequence for the five portions of the Mc1r gene provided. (Note: You are only transcribing short portions of the DNA sequence for this protein. The actual gene contains 954 base pairs.) 3. Using the mRNA sequence completed in Step 2, determine the resulting amino acid sequence of the MC1R protein. (Note: You are translating only a portion of protein. The full protein is 317 amino acids long. The numbers above the columns in the tables indicate amino acid positions in the protein sequence.) You may use the genetic code chart provided in your textbook or the one on page 6 of this handout. 4. There are five substitution mutations in the dark-colored mutant Mc1r gene. Compare the DNA sequence of the light-colored wild-type Mc1r gene with the DNA sequence of the dark-colored mutant Mc1r gene. Indicate the locations of the five mutations by circling the five single DNA nucleotides that are mutated in the mutant Mc1r gene table. 5. Using the information in the introduction, determine whether each of these mutations is a silent, missense, or nonsense mutation. a. Using the mutant Mc1r gene data, shade in the columns (including DNA, mRNA, and amino acid) in gene table 2 that contain a silent mutation using a BLUE colored pencil. b. Likewise, shade in the columns that contain a missense mutation using a RED colored pencil. c. Shade any columns that contain nonsense mutations using a GREEN colored pencil. 6. Answer the questions following the gene tables.

TTG AGG TGG GCG TGT CCG CAA GGA CGG GAC CGG TGG GCC CAC TGA CAC TCA TAA CAC TGT GAC GGG GCC CGA GTG TAC GAA CGT GAA CAG GTG GTT CCA AAG GCT GAG

TTG AGG TGG ACG TGT CCG CAA GGA CGG GAC CGG TGG ACC CAC TGA CAC TCA TAA CAC TGT GAC GGG ACC CGA GTG TAC GAG CGT GAA CAG GTG GTG CCA AAG GCT GAG

https://www.biointeractive.org/sites/default/files/Mouse-Molecular-Genetics-Student-Activity-1.pdf

Genetic variation can result from mutations caused by environmental factors.

Rock Pocket Mouse