Epistasis meaning and explanation
Epistasis = Interaction of different gene loci.
One gene locus masks or surpresses the expression of another gene locus.
The genes involved may control the expression of 1 phenotypic characteristic by either:
- Working AGAINST each other (ANTAGONISTICALLY) resulting in masking.
- Working TOGETHER in a complementary fashion.
- Homozygous presence of a recessive allele may prevent expression of another allele at a second locus.
- Alleles at 1st locus are epistatic to alleles at the 2nd locus (hypostatic).
Epistasis reduces phenotypic variation.
Recessive and dominant epistasis
- E.g. a homozygous aa may be epistatic to alleles of the gene B/b.
- Neither the B or the b can be expressed if there is no dominant allele A present.
- Occurs when a dominant allele at one gene locus masks the expression of the alleles at a 2nd gene locus.
- E.g. two gene oci D/d and E/e. Presence of one D alleleresults in whire fruits regardless of the aleles present at the 2nd locus.
Working in a complementary fashion:
- The way 2 gene loci may produce these results is if they compliment each other.
- If one gene codes for an intermediate colourless pigment and the second locus codes for an enzyme that converts the intermediate compound to the final purple pigment.