How is mouse coloration inherited? - briefly
Mouse coat color is controlled by several genes that obey Mendelian inheritance, with dominant, recessive, and epistatic effects influencing the phenotype. Important loci such as Agouti (A), Extension (E), and Mc1r combine to produce patterns including albino, black, brown, and agouti coats.
How is mouse coloration inherited? - in detail
Mouse coat color is determined by multiple genes that interact in Mendelian and non‑Mendelian patterns. The primary pigment types are eumelanin (black/brown) and pheomelanin (red/yellow). Production of each pigment is regulated by the melanocortin‑1 receptor (Mc1r) pathway; functional Mc1r favors eumelanin, while loss‑of‑function alleles shift synthesis toward pheomelanin.
Key loci include:
- Agouti (A): Dominant allele produces a banded hair pattern, limiting eumelanin to the hair tip. Recessive a allele yields uniform eumelanin, resulting in solid black or brown coats.
- Extension (E): Dominant E permits melanocyte activity; recessive e restricts melanin production, creating albino phenotypes when combined with other mutations.
- Dilution (D): Dominant D yields full pigment intensity; recessive d reduces pigment density, producing blue (diluted black) or lilac (diluted brown) shades.
- Tyrosinase (Tyrc): Mutations impair melanin synthesis, generating albino or partial albino variants.
- K locus (K): Dominant K allele induces dominant black, overpowering other color genes; recessive k permits expression of underlying patterns.
Inheritance follows classic dominance relationships, but epistatic interactions modify outcomes. For example, the albino e allele is epistatic to Agouti, masking any banded pattern. Compound heterozygosity at multiple loci can produce intermediate phenotypes such as sable (agouti combined with a dilution allele).
Sex‑linked and autosomal loci also contribute. The X‑linked M (mouse coat color) gene influences pigment density, with males expressing the phenotype when hemizygous. Autosomal recessive mutations, such as c (copper) and h (hairless), affect melanin distribution and hair structure, respectively.
Quantitative traits, like the extent of pigment dilution, involve polygenic modifiers. These modifiers fine‑tune melanin concentration and can be mapped through quantitative trait locus (QTL) analysis.
In laboratory strains, controlled breeding demonstrates predictable segregation ratios: a cross between heterozygous Agouti (A/a) and recessive albino (e/e) parents yields a 1:1 ratio of agouti to albino offspring, confirming Mendelian inheritance. Multi‑locus crosses produce more complex ratios, requiring calculation of each gene’s contribution and epistatic hierarchy.
Overall, mouse coat coloration results from a network of dominant, recessive, and epistatic alleles across several loci, each influencing melanin synthesis, distribution, and intensity. Genetic analysis and controlled breeding experiments elucidate these relationships, enabling precise prediction of phenotypic outcomes.