The Base Loci
Every mouse starts with a number of genes that determine what the mouse looks like. This structure consists of at least 5 basic color genes. Each gene consists of 2 alleles. There are recessive and dominant alleles, which are often indicated by the use of uppercase and lowercase letters within the A locus (uppercase = dominant, lowercase = recessive). Uppercase and lowercase letters are also used to make visible Wildtype allele (mutation not present, Capital letter) & Mutated allele (mutation present, lowercase letter) Both recessive and dominant genes have either a heterozygous gene or a homozygous gene. Heterozygous means that the animal has only one mutated allele of colors or coats (a non-identical pair). Homozygous means that the animal has a two-piece set of this color or coat (an identical pair). Each animal receives 1 random allele from each of the parent animals at each locus present (described below). Dominant alleles are visible in both heterozygous and homozygous form. Recessive alleles are only visible in homozygous form. Dominant alleles are therefore dominant over recessive alleles.
Mouse-Info 