What is the difference between epistasis and dominance?

Answer 1

In dominant epistasis a F2 cross yeilds a typical 12:3:1 ratio. Of the two genes controling the phenotype one is termed the epistatic gene and must be present in homozygose recessive form before the second genes the hypostatic gene, alleles will be expressed in the phenotype. If it helps to think about it one gene is "stronger" than the other and both alleles for the strong gene must be recessive before the second gene gets a chance to alter phenotype.

Answer 2

Recessive epistasis yields and typical 9:3:4 ration in the second filial cross. The epistatic gene if present in homozygous recessive form will stop the expression of the hypostatic dominant allele. This is typically seen for biochemical pathways where the the epistatic gene produces a product which is further converted by the hypostatic gene.

Answer 3

In dominant suppression epistasis the dominant form of a gene inhibits the expression of another gene. A dihybrid cross between two heterozygous parents will produce an F2 ration of 13:3. For example:

In feather colour of chickens the presence of the dominant allele I inhibits the expression of a second gene, C, coding for colour at another locus. Therefore:

C_= colour

cc = white

I_ = inhibitor

ii = no effect

Chickens will only be coloured if the inhibitor gene is homozygous recessive (ii) and there is at least one C allele. Its genotype would therefore be either iiCC or iiCc.

The chickens will however be white if the inhibitor gene is present, or if the dominant allele for colour is not present. Possible genotypes for white chickens are therefore I_C_ or I_cc or iicc.

Hope this helps you :)

Answer 4

When a recessive at either locus masks the affects of the dominant phenotype at the other locus.

So AA will stop the expression of B, and bb will stop the expression of A.

This means that A-;bb, AA;B- and AA;bb will all have the same phenotype.

Answer 5

Dominance is between alleles of

homologous genes

;

epistasis

is "dominance" of one non-homologous allele over another.

If R →

red flowers

and r → white flowers, any plant with the genotype Rr will have red flowers, because R is dominant over its homologous allele, r. But if a C allele is required for R to produce red flowers, it is a case of epistasis, because, even thought the C allele is not a flower-color allele, it is required for the R allele to be expressed.

Answer 6

in dominane phisiological effect of allele over other allele is on the same loccus while in epistasis on different loccus