Final answer:
In genetics, the -/y notation indicates a male organism that carries the mutant allele of a gene on the single X chromosome. Epistasis can influence gene expression, where one gene masks the effects of another, as seen in mouse coat colors. X inactivation balances the dosage of X-linked genes between males and females, leading to mosaicism in females with heterozygous X-linked traits.
Step-by-step explanation:
In genetics, the -/y notation refers to the sex chromosomes in organisms that use XY sex-determination system, such as humans and most other mammals, including mice. The X chromosome can carry mutations, and different configurations of these mutations are represented by symbols like '+', '-', 'm', and others. Females have two X chromosomes (XX) and can be homozygous (+/+ or -/-) or heterozygous (+/-) for a gene, while males have one X and one Y chromosome (XY), so they will be hemizygous for a gene on the X chromosome, represented as -/y if they carry the mutant allele, or +/y if they carry the wild-type allele.
Furthermore, a gene at a separate locus can affect the expression of other genes, in a phenomenon known as epistasis. For example, mouse coat color is influenced by the C gene, where the dominant C allele is necessary for pigment production, and the recessive c allele results in an albino phenotype, regardless of other color-related genes. This demonstrates the epistatic relationship where one gene masks the expression of another gene at a different locus.
Additionally, X inactivation plays a critical role in organisms with multiple X chromosomes, such as female mammals. This process ensures that females, with two X chromosomes, do not have twice the dose of X-linked gene products as males, which only carry a single X chromosome. The random inactivation of one X chromosome in each cell during embryonic development leads to a mosaic expression of X-linked genes, as seen in the coat colors of tortoiseshell cats.