Final Answer:
The methylation state of the agouti gene promoter for this mouse is:
B) Partially methylated
Step-by-step explanation:
The agouti gene plays a crucial role in determining coat color in mice. In the context of a mouse with the avy allele expressing a dark brown phenotype, the best description of the methylation state of the agouti gene promoter is "Partially methylated."
Methylation refers to the addition of methyl groups to DNA, which can regulate gene expression. In this case, the presence of the avy allele leads to a dark brown phenotype, indicating that the agouti gene is not fully methylated (A), as complete methylation typically results in a suppressed or "silenced" gene.
Conversely, an unmethylated state (C) would likely lead to a different phenotype, given that agouti gene expression is associated with the production of a yellow pigment. The dark brown phenotype suggests that some level of methylation is occurring, but it is not complete.
Therefore, "Partially methylated" (B) is the most accurate description, indicating a balance between methylated and unmethylated states, allowing for the expression of the agouti gene and the observed coat color. The specific degree of methylation may vary among individual mice, contributing to the range of coat colors observed in the population with the avy allele.