Interactions Between Gene Pairs
Epistasis: is a condition in which one gene pair masks the expression of another gene.
Genes at one locus that affect the expression of genes at a different locus are said to be
epistatic. Hair color in mammals is an example. The black, brown, or yellow fur color in
Labrador retrievers is the result of variations in
the amount and distribution of the pigment melanin. Two genes are involved. The alleles of one
gene control the production of melanin (black and brown). Two alleles - B (black) is dominant
over b (brown). The other gene influences melanin deposition (less of the pigment results in the
yellow color). Two alleles - E promotes pigment deposition and is dominant over e.
A black coat must have at least one dominant allele at both loci
BBEE, BbEe, BBEe, or BbEE. A brown coat results from bbEE, or bbEe. A yellow coat results from
Bbee, BbEE, or bbee.
Albinism is a phenotype that results when the pathway for melanin production is completely blocked.
The genotype is homozygous recessive at the gene locus that codes for tyrosinase, an enzyme in the
melanin-synthesizing pathway.
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