Epistasis

Epistasis is a biological phenomenon where the effect of one gene (the epistatic gene) is dependent on the presence of one or more 'modifier genes'. It describes the interactions between genes that result in a specific phenotypic outcome. This interaction can suppress the effect of other genes (hypostasis), enhance it, or alter the expression in complex and varied ways. Epistasis plays a crucial role in determining inheritance patterns, phenotypic ratios and genetic interactions. It is not simply a matter of additive effects; instead, the phenotype reflects the interplay of gene products with the expression of a gene depending upon the allelic composition of another gene.

Epistasis meaning with examples

• In Labrador retrievers, the gene for coat color (B) is epistatic to the gene for fur pigment deposition (E). If a dog has the ee genotype (e.g., Labrador with the 'yellow' coat), it won't produce any black pigment, regardless of the alleles at the B locus (which codes for black or brown pigment), because the epistatic 'e' allele prevents the color deposition regardless of the underlying color determination.
• In sweet pea flowers, two independently assorting genes are involved in pigment production. One gene (C) determines the production of a pigment precursor, while another gene (P) determines the enzyme converting the precursor to pigment. If an individual is recessive for either gene, then no pigment will be formed, because production is stopped at a preceding stage of the pathway. This illustrates recessive epistasis.
• Consider an example of reciprocal recessive Epistasis in squash fruit color. Two genes are involved, with homozygous recessive conditions at either gene suppressing the pigment formation. 'aa' or 'bb' will both results in a white squash, regardless of the alleles at the other gene locus, effectively eliminating all pigment formation. Only the genotype 'A-B-' shows colored fruit; all others are white.
• In fruit flies, the expression of a gene can be masked or modified by another gene or its product in the genome. The development of eye color, for instance, is a multigenic process and mutations in one gene might alter expression in other eye pigment genes. Epistasis also describes complex scenarios in pathways that lead to various physical aspects or even biological process, which is essential to understanding genetics.