Final answer:
The selection coefficient against a light phenotype in mice considers the genetic factors governing coat color and the environmental pressures that favor certain phenotypes. Due to predation risks associated with non-camouflaged intermediate coat colors, light-colored mice would not be favored to transition towards darker coloration, despite dark-colored mice potentially having a higher overall fitness.
Step-by-step explanation:
The selection coefficient against a light phenotype in mice living in a specific environment can be interpreted by examining how mice with different coat colors fare in their habitat. These mice exhibit a phenotypic ratio that is determined by their genetics. Specifically, the mottled agouti coat color (A) is dominant over solid colorations like black or gray. A separate gene (C) is responsible for pigment production where the recessive c allele leads to albinism in the homozygous recessive cc genotype. This condition is termed epistasis, where the C gene is epistatic to the A gene.
In the context provided, lighter-colored mice would not be selected for darker coloration because individuals that might transition towards a darker coat would actually be less fit compared to those retaining a light color. This is due to the fact that an intermediate coloration would be highly detrimental, as mice with such coats cannot camouflage effectively in either sand or grassy patches, increasing their susceptibility to predation.
Natural selection and its constraints, such as the trade-off between immediate and progressive color changes, factor heavily in determining the prevalence of certain traits like coat color in mice living in a particular habitat. In this example, natural selection is constrained by polymorphisms that render intermediate phenotypes less beneficial. Hence, the selection coefficient against a light phenotype would indicate how disadvantageous being light-colored is in a specific environment, considering the camouflage requirements.