= the interaction of different gene loci so that one gene locus masks or suppresses the another gene locus
Epistasis is not inherited, it is an interaction between two gene loci. It reduces phenotype variation.
The genes involved can control the expression of one phenotypic characteristic in one of two ways:
1. They may work against each other (antagonistically) resulting in masking.
2. They may work together in a complementary fashion.
The homozygous presence of a recessive allele may prevent the expression of another allele at a second locus.
The alleles at the first locus are epistatic to the alleles at the second locus, which are described as hypostatic.
Example - the inheritance of flower colour in Salvia
- Two gene loci, A/a and B/b, on different chromosomes are involved.
- A pure-bred pink Salvia, genotype AAbb, was crossed with a pure-bred white Salvia, genotype aaBB. All the F1 generation, genotype AaBb, had purple flowers.
- Interbreeding the F1 results in purple, pink and white flowers in the ratio 9:3:4 in the F2 generation.