Epistasis: Definition, Meaning Types, Examples, Causes, Explanation

What Is Epistasis?

Epistasis therefore is a gene interaction that may suppress the effects of a gene by another gene. This concept is critical in dealing with genetics since it aids in understanding how various genes can make organisms develop various characteristics that cannot be foretold based on the features of different genes.

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Epistasis is significant in the knowledge of the broader picture of genetics and the ways through which it is inherited. In this article, the subject of gene interactions will be briefly discussed aiming to give important information to the reader about the epistasis model and how it complicates the expressions of certain traits.

Basic Concepts

The genetics related to this topic involve the basics of genes, alleles, genotype, phenotype, and the relationship between them in explaining how traits are inherited and expressed.

Gene: Definition And Function

A gene is a section of DNA that contains information on the production of proteins or RNA, these being essential components of an organism’s formation and operations. These hereditary units influence many characteristics and biological phenomena by dictating the synthesis of molecules, specifically proteins, which execute certain tasks in cells.

Alleles: Dominant And Recessive

Alleles are other forms of a single gene that are brought about by mutation of the genetic material. The result shows that dominant alleles hide recessive alleles in a heterozygous person. For instance, if a gene contains a dominant allele for brown-eyed and a recessive allele for blue-eyed, then the characteristic owned by the brown allele will be inherited.

Genotype Vs. Phenotype

Genotype can be described as the total of genetic factors followed by an organism or the sum of allelic components for a given gene. carrying genotype in combination with a certain environment produces the manifestation of the phenotype or the physical trait. For instance, BB or Bb genotype may give a phenotype of brown eye colour.

Types Of Epistasis

Epistasis are classified as:

Recessive Epistasis

Recessive epistasis is said to occur when a recessive gene in an organism affects the manifestation of genes located at other regions of the same chromosome. This indicates that an organism that is homozygous for a gene can hinder the phenotype that is linked with another gene.

Examples: In Labrador retrievers, coat color is therefore controlled by two genes meaning that the color of the coat you find attractive will be controlled by these two genes. The E gene contributes to colour and the B gene is related to black/brown. At locus E, the non-expression of the B gene due to the recessive e allele leads to the yellow coat colour as it does no matter the status of the B allele.

Dominant Epistasis

Dominant epistasis happens when a dominant allele at a particular locus overrides the impression of alleles at the other locus. The first gene means that the gene submits the other gene’s work and always controls the phenotypes, be it with a dominant or recessive allele.

Examples: In the case of squash fruit colour the alleles present in one locus W are capable of overwhelming or effectively hiding the wild-type allele gene Y. Any plant that has at least one megasporangium W allele will produce white squash, the colour of the fruit depending on the number of recessive w alleles and dominant Y alleles.

Duplicate Recessive Epistasis

The recessive epistasis deal represents a case when one of the two different recessive genes can hide another gene. Since phenylketonuria is dominant both genes require the presence of at least one dominant allele; otherwise, the recessive alleles at that particular loci will nullify the expression of this trait.

Examples: ATD and TAD can lead to albino conditions in plants and selfishness of recessive alleles at either of the two different loci. If a plant inherits an indicator other than a dominant allele at both the loci, then it will be an albino irrespective of the other alleles being a feature of the plant.

Duplicate Dominant Epistasis

Dominant duplicate epistasis takes place when a dominant allele at one locus can suppress a second gene at another locus. The dominant allele at either of the loci prevents the expression of the trait; the presence of one gene with one of its alleles produces the same phenotype independent of the other gene’s alleles.

Examples: In fruit shape, in shepherd’s purse, the complete dominance of alleles at one of the two loci, causes an absolute expression of the specific trait of that locus, thereby obliterating the effect of alleles at the other locus. Organisms which are heterozygous or carry the dominant allele at either the l or LOCI will exhibit the dominant trait of fruit shape.

Complementary Gene Interaction

Complementary gene interaction takes place when two different;

traits are the complex result of several genes that need to act in harmony in the process of synthesizing a particular characteristic. Homozygous dominant alleles of both genes are required for the phenotype to be expressed; if one of the genes contains recessive alleles there is no phenotype.

Examples: In flower color in sweet peas therefore the C gene which determines color and the P gene which determines pigment must both be dominant. Flowers will be white if both genes are recessive or if only one of them is recessive because the other will be dominant.

Case Studies

A Few detailed examples to understand epistasis are:

Detailed Case Study 1: Coat Color In Mice

The coat color in mice is polygenically determined which proves the presence of various forms of gene interactions. There is, for instance, recessive epistasis that includes the Agouti and Extension genes or loci. The A gene controls where the pigment is delivered and the E gene controls the production of the pigment.

If the mouse were created from a matting of two heterozygous mice that had the recessive e allele, the mouse would still have a yellow coat even if it had two dominant non-yellow genes at the A locus. On the other hand, the dominant E allele enables the A locus to produce black/brown pigments. Such an interaction provides an example of how recessive epistasis can hide the other genes and their impact on the final phenotype.

Detailed Case Study 2: Human Eye Color

Eye colour in human beings is a classic example of a polygenic trait or one that is controlled by multiple genes. The diagnostically most imperative gene groups for eye colour are OCA2 and HERC2. Changes in these genes range from blue-eyed to green-eyed to even brown-eyed individuals is thus due to this belief.

These genes work synergistically and, therefore, their allelic variations are additive, formerly, different sets of alleles of these genes contribute to the existing variety of eye colour. For instance, multiple dominant alleles for brown eyes will cause the frequency of brown eyes plus multiple recessive alleles for light-coloured eyes will also lead to light-coloured eyes.

Detailed Case Study 3: Flower Color In Morning Glory

That means that in Morning Glory, flower colour is brought about by gene complementary. Thereby, to have part or full-coloured flowers the ‘C’ gene for colour and the ‘P’ gene for pigment production must possess at least one dominant allele. If either of the genes has the recessive alleles, that is cc or pp, the flowers will be white. This often-used interaction shows how two different genes can combine to give one characteristic. This case study brings out the factor of complementary gene interaction in which the phenotypic character is only observed when both genes possess dominant alleles.

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