In the hybridization of 2genes (4 different alleles, 2 ofeach pair) how does epistasisaffect the proportion ofphenotypical forms in the F2generation?
In the hybridization of 2
genes (4 different alleles, 2 of
each pair) how does epistasis
affect the proportion of
phenotypical forms in the F2
generation?
The Dihybrid cross is crossing between two organisms, being heterozygous to two different traits. Dihybrid means the presence of two traits with two different alleles per trait. In a dihybrid cross, the first filial generation(F1) produces four identical offsprings. whereas the second filial generation(F2) that occurs by the crossing over between the members of the F1 generation shows phenotypic ratio 9:3:3:1. The 9 represents individuals with dominant traits, 3 represents individual with a first dominant and second recessive trait, other 3 represent individual display first recessive and second dominant traits, and finally, 1 represents both negative traits.
Epistasis is a phenomenon in which the effect of a mutation is dependent upon one or more other genes called modifiers. Epistasis means the effect of a gene variant is masked or unmasked by that of a different gene.
Epistasis could be of following types-
Recessive masking epistasis- Homozygous recessive gene masks the effect of other genes no matter if present in the dominant or recessive form.
for eg BE is responsible for black color and bbE is for the brown color and ee is a yellow color. If the generation acquired homozygous recessive genotype for E gene i.e. ee, the resulting phenotype will always be yellow doesn’t matter if the genotype for B gene is recessive or dominant.
Dominant masking epistasis- dominant For eg- G is for grey color, gg is for not grey, ggE is black color and ggee is a chestnut color. If the generation has genotype G then the progeny will be grey at maturity as G will mask the other gene but if the progeny has gg then the phenotype of the other gene will be expressed.
Modifying epistasis- For eg- BD is black, bbD is red, Bdd is blue and bbdd is a frown. In this case, the recessive genotype bb modifies the expression of the recessive genotype of the D gene causing fading of colors.
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