How is coat color inherited in these mice? - briefly
Coat color in these mice is governed by Mendelian alleles, where a dominant pigment allele masks a recessive albino allele, and heterozygotes display the dominant hue. The phenotype of each offspring is predicted by the combination of parental alleles according to classic dominant‑recessive segregation.
How is coat color inherited in these mice? - in detail
Mouse coat pigmentation follows classic Mendelian patterns, modified by multiple loci that interact through dominance, recessivity, and epistasis. The primary genes include Agouti (A), which determines the distribution of black and yellow pigments; Extension (E), controlling the production of eumelanin; Brown (B), converting black eumelanin to brown; and Albino (c), a recessive allele that blocks all pigment synthesis.
When two heterozygous individuals (A a, E e, B b) are crossed, the expected phenotypic ratios derive from independent assortment of each locus. For example, a cross between A a E e B b and a, a, e, b yields:
- 9/16 displaying the agouti pattern (A‑), with black or brown eumelanin depending on the B allele;
- 3/16 showing a solid black coat (aa E‑ B‑);
- 3/16 exhibiting a brown coat (A‑ E‑ bb);
- 1/16 appearing albino (c c).
The Extension locus is epistatic to Agouti: an ee genotype eliminates eumelanin, producing a yellow coat regardless of the A allele. Similarly, the Albino allele is completely recessive and masks all other color genes when homozygous.
Sex-linked inheritance plays a minor role; the K locus on the X chromosome influences the presence of a dominant black coat in some strains, resulting in different expression between males (XY) and females (XX).
Molecularly, each gene encodes enzymes or regulatory proteins in the melanogenesis pathway. Mutations that reduce enzyme activity or alter transcription factor binding change pigment type or amount, leading to the observable coat colors.
Key points for predicting offspring color:
- Identify parental genotypes at each relevant locus.
- Apply Mendelian segregation for each gene.
- Account for epistatic relationships: c overrides all, e suppresses eumelanin, B modifies black to brown.
- Consider sex chromosome effects when X-linked loci are involved.
Accurate prediction requires genotyping or phenotypic assessment of parents, followed by calculation of expected ratios using Punnett squares or probability tables.