Question

Definition of Epistasis.

Answer 1

Hint The process of genetics in which the presence or absence of one gene affects the gene mutation, or one gene masks the effect of another gene. It generally means masking the effect of one gene by another.

Complete answer:
Epistasis is adapted from Greek meaning “standing upon.” The alleles that are being masked or silenced by other alleles are said to be hypostatic while those alleles that are doing the masking are called the epistatic alleles. The interaction between the two or more loci is called epistatic interaction.
There are two types of Epistasis: Dominant epistasis and recessive epistasis.
Dominant epistasis occurs when the dominant allele of one gene (dominant) masks the effects of either allele of the second gene. The homozygous recessive expression of the A gene (aa) together with the homozygous dominant or heterozygous expression of the B gene (BB or Bb respectively) generates yellow fruit. The aabb genotype (recessive for gene A and B) produces green fruit. Now if a dominant copy of the A gene is present in the homozygous or heterozygous form, the white-coloured fruit will be produced regardless of dominant B genes.
In the recessive epistasis process, when recessive alleles at one locus mask the expression of each (dominant and recessive) alleles at another locus. This sort of cistron interaction is additionally called a supplementary organic process. A decent example of such cistron interaction is found for grain change maize.
During this form of the epistasis process, a dominant gene at one locus will mask the expression of each (dominant and recessive) alleles at the second locus. This can be conjointly called inhibitory gene interaction. An associate degree example of this sort of gene interaction is found for anthocyanin pigmentation in rice.

Note:
Epistasis is adapted from Greek meaning “standing upon.” When a dominant allele (gene A) masks the activity of another allelic pair (Bb) it is called dominant epistasis. The phenotypic ratio in ${F}_{2}$ generation is 12:3:1 or 13:3. In presence of only the recessive allele, the activity of A is masked. The phenotypic ratio in ${F}_{2}$ generation is 9:3:4.