What Is Epistasis

Genetics involves a phenomenon, epistasis, wherein the effect of a gene mutation is dependent on the presence or absence of mutations in one or more other genes, known as modifier genes. Thus, epistatic mutations have different effects when they occur alone than when they occur together. Epistasis is especially used to show that the effect of a gene variant is hidden by other genes.

There is a renewed appreciation for both the importance of studying gene interactions and to answer questions in a coordinated quantitative manner with the advent of high throughput functional genomics and the emergence of systems approaches in the field of biology. This is accompanied by the newfound ability to trace the genetic basis of evolution to the specific molecular changes, which are fundamentally significant to understand the role and structure of genetic pathways and the evolutionary dynamics of complex genetic systems.

Consequently, Epistasis is an interaction discussed at the phenotypic level of the organization. Genes at a particular epistatic interaction can exhibit independent assortment at the genotypic level, in which case the phenotypic ratios can seemingly deviate from those that are expected with independent assortment.

An Overview of Epistasis

Typically, epistasis assists in describing various phenomena such as functional interaction between genes, statistical deviation from additive gene action, and genetic outcome of mutations that act in the same genetic pathway.

Epistasis analysis has been traditionally used to order genes in developmental and metabolic pathways. However, with the emergence of high-throughput genetic screens, this approach has become more organized, particularly in yeasts. Studies have demonstrated that gene interactions are widespread, and their analysis can be beneficial in understanding the structure of intricate genetic networks.

A major disadvantage of this comprehensive examination of gene interactions is the sheer amount of interactions that need to be tested, which is known to increase exponentially with the number of genes. Additionally, epistasis can make it difficult to determine the genetic basis of complex traits in a natural population. The effects of multiple QTLs can be obscured by their interactions with other loci, thus making mapping difficult.

Epistasis in human genetic diseases is common, and there are some examples wherein the serviceable footing of a specific interaction has been illustrated. Additionally, epistasis emerges as a natural repercussion of the process of evolution, as all resultant changes due to evolution are based on genetic alterations that have previously taken place.

Also Explore:

| Mutation: Principles of Inheritance and Variation |

| Molecular Basis of Inheritance |

Types of Epistasis

Epistasis gene interactions are of 6 types

Dominant

Recessive

Polymeric Gene Interaction

Dominant Inhibitory

Duplicate Recessive

Duplicate Dominant

It is an example of simple or dominant epistasis when a dominant allele masks the expression of both recessive and dominant alleles at different loci.

It is a recessive epistasis when the recessive allele conceals the expressing.

It is suppression epistasis or dominant inhibitory when genes conceal other genes by suppression. It is a result of genes acting as suppressors or a component inhibiting the expression of other alleles.

Duplicate epistasis is based on two loci. When a recessive allele is present at both loci, it is referred to as duplicate recessive epistasis. This is also known as complementary gene action, as both genes are necessary for the correct phenotype to be expressed. Conversely, when a dominant allele is present at both loci, it is referred to as duplicate gene action or dominant epistasis, as the dominant allele is masking the expression of the recessive allele.

The polymeric gene interaction is when two dominant alleles are combined, either strengthening the phenotype or creating a median variation. When these dominant alleles are on their own, they generate a physical characteristic that differs from when they are united. This results in three phenotypes being created from just two dominant alleles.

Epistasis - Example

Primula, a plant, produces Malvidin, a chemical. The production of Malvidin is determined by the K gene, which is a dominant characteristic. The suppression of its production is regulated by the D gene, which is also a dominant characteristic. Even when the dominant K allele is present, there is no expression of the dominant D allele. This interaction of alleles can be classified as a dominant inhibitory type of epistasis, as the dominant D allele inhibits the K allele.

In summer squash, the color white is dominant over green and yellow, which is an example of dominant epistasis.

Frequently Asked Questions

What is Dominant and Recessive Epistasis?

Epistasis is a phenomenon in which the effect of one gene is dependent on the presence of one or more other genes. In dominant and recessive epistasis, the phenotype of an organism is determined by the interaction of two or more genes. Dominant epistasis occurs when the phenotype of the organism is determined by the presence of one dominant gene, while recessive epistasis occurs when the phenotype of the organism is determined by the presence of two recessive genes.

When a dominant allele conceals the expression of both recessive and dominant alleles at other loci, it is called dominant epistasis. On the other hand, when the recessive allele masks the expression, it is called recessive epistasis.

Epistasis is a phenomenon in which the effect of one gene is dependent on the presence of one or more other genes, while dominance is a phenomenon in which one allele of a gene is expressed more strongly than another allele of the same gene.

Epistasis is a relationship between alleles of two different genes, whereas Dominance refers to the relationship between two variants or alleles of the same gene.

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