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Epistasis


There are cases where alleles of one gene inhibit the action of alleles of another pair, which may or may not be on the same chromosome.

This phenomenon is called epistasis (from Greek epi, about and stasis, stop, inhibition). The gene that exerts the inhibitory action is called epistatic, and what suffers the inhibition is called hypostatic.

If the epistatic gene acts in a single dose, that is, if the presence of a single epistatic allele is sufficient to cause hypostatic inhibition, then there is talk of dominant epistasis. On the other hand, if the allele that determines epistasis acts only in double dose, it is recessive epistasis.

Ordinary mice can have three different coat colors:

  • black;
  • albino;
  • aguti.

These phenotypes are determined by two interacting gene loci. Let us separate the loci to understand the phenomenon: the locus that determines the color of the coat has been baptized as THE. When the genotype of the individual is THE_ (this trait can mean A or a), it will display the color aguti and when it is aa the individual will have the hair black. The other locus only controls the expression of locus A. Whenever the individual's genotype is P_, it will display the phenotype determined by A, and when the genotype is pp, the individual will be albino, regardless of genotype for locus THE.

Take a look at the intersection and see how this interaction works:

Note that the only "function" of the P locus is to control the expression of A. Thus, it is only possible to know an individual's genotype for the P locus if it is albino, in which case it is impossible to predict the genotype for allele A.

This is a classic example of Epistasis. In this case it is called Recessive Epistasis, since it occurs when the epistatic locus influences the other when it occurs in recessive homozygosis.

Remembering: Epistasis is defined as the interaction where alleles of one gene pair inhibit the action of alleles of another pair, which may or may not be on the same chromosome.

An example of dominant epistasis

There is another type of epistasis, which is called Dominant Epistasis. As you can imagine, this type of epistasis occurs when the epistatic locus influences the other by presenting at least one dominant allele.

The color of plumage in chickens is determined by two loci. One determines the color itself and the other controls the action of the former (do not forget that this is an example of epistasis). The allele Ç conditions colorful plumage and ç White plumage. These alleles interact with the alleles I and iso that if an individual has an allele I In the genotype, his coat will be white.

So only genotype birds C_ii They are colorful. The ccii birds are white because they do not have the pigment allele (Ç) and the birds C_I_ they are white because allele I prevents pigmentation. Just the chicken has allele I in its genotype (_ _ I _) so that no pigment is produced. Therefore, the epistatic gene I acts in a single dose, behaving as if it were dominant. Hence this type of gene interaction is known as dominant epistasis.

CIcICici
CI

CCII

White

CcII

White

CCIi

White

CcIi

White

cI

CcII

White

ccII

White

CcIi

White

ccIi

White

Ci

CCIi

White

CcIi

White

CCii

Colorful

Ccii

Colorful

ci

CcIi

White

ccIi

White

Ccii

Colorful

ccii

White

F2