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.

PREVIOUS

END OF LECTURE 6

LECTURE 6 INDEX

MAIN INDEX