Introduction
Epistasis is a phrase which has been used to describe a wide range of occurrences, such as the genetic consequence of mutations which acts along the same genetic pathway, the functional interaction of genes, and the statistical divergence from additive gene action.
Epistasis
Mendel’s pea plant research suggests that the genes (or unit factors, as he named them) governed the sum of an individual’s phenotype, and that each trait was distinctly & completely regulated by a single gene. In fact, many genes (each one with two or more alleles) functioning in concert virtually always influence single observable features. In humans, for instance, at least 8 genes influence eye colour.
Several genes can sometimes contribute to parts of a similar phenotype despite their genetic variants ever interacting directly. Genes may be expressed consecutively in the case of the organ development, with each gene contributing to the organ’s complexity and specificity. Genes may work in a complimentary or synergistic manner, requiring the expression of two or more genes at the same time to alter a phenotype. Genes can also work in opposition to one another, with one gene influencing the expression of another.
In epistasis, genes have a hostile connection, with one gene concealing or interfering with the expression of the other. The word epistasis is Greek in origin and means standing on. The masked or muted alleles are hypostatic to the epistatic alleles that perform the masking. A gene network where the expression of one gene is dependent on the activity of a gene which comes before or after it in the pathway is often the biochemical basis of epistasis.
Types of Epistasis
Dominant epistasis
Epistasis dominant occurs when a dominant allele at one location is able to hide two alleles (dominant and recessive) at a separate locus. This indicates that a dominant gene blocks the expression pattern of one dominant or recessive allele. This is also regarded as the simple epistasis.
Duplicate epistasis
Epistasis with duplicate dominance occurs when a dominant allele at one of two loci has the ability to inhibit recessive alleles present at both loci. Double gene activity is another name for this phenomenon. The awn feature observed in rice is a great example of epistasis with the dominant duplication. Two duplicate genes which predominate in rice can affect awn formation (A and B).
Recessive epistasis
The field of recessive epistasis refers to when recessive alleles from one location inhibit their expression by producing both (dominant and recessive) alleles at the other site. Epistasis with addition is another name for this type of gene interaction.
Dominant Inhibitory
In this sort of epistasis, a dominant allele at one locus can be blocked from expressing by both (dominant and recessive) alleles at secondary locus. An inhibitory gene interaction is another name for this.
Polymeric Gene Interaction
When two dominant alleles are separate, their effects are similar, but when they are combined, their effects are larger. The word polymeric gene interaction is used to describe this form of gene interaction. The cumulative effect of two alleles is thought to be cumulative or additive, however because the two genes have complete dominance, they cannot be regarded as additive genes. Genes do not demonstrate dominance in the case of additive effects.
Duplicate recessive epistasis
Epistasis with duplicate recessive alleles occurs if recessive alleles through one or both loci can hide the dominant alleles at the two loci. Epistasis complementarity is another term for this.
Examples of Epistasis
Primula is a plant that generates the chemical malvidin. Malvidin synthesis is controlled by the K gene, while inhibition is controlled by the D gene. The D and K genes have a dominant influence on each other. There is no evidence of a dominant D allele in the presence of a dominant K allele. Since the dominant D allele obstructs the K allele, this interplay of alleles is characterised as dominant inhibitory epistasis.
Conclusion
Epistasis is a non-Mendelian inheritance pattern in which one gene can interfere with the expression of another. This is frequently seen in gene circuits in which the expression of one gene is directly influenced by the absence or presence of another gene product in the pathway.