2. In class we discussed a case of epistasis that occurs in the determination of

Question

2. In class we discussed a case of epistasis that occurs in the determination of sweet pea color. Another example occurs in the determination of blue petal color in the Priemda plant Blue pigment (malvidin production is catalyzed by the product of the K gene (functional wild type protein is fully dominant to the mutant null allele Lack of malvidin results in white petals Expression of the A gene is controlled by the gene product of the D gene. Wild type D fully represses expression of K and is fully dominant to d. K and D are on separate chromosomes in Primula. What will he phenonpic ratio of oflTspring be for a cross between KKDd plants?int: figure out the different possible genotypes and then figure out the phenotype for each genotype) Which alleler's) are epistatic to which alleleis)? Hint: think about the definition of epistasis). thibito

Explanation / Answer

Parental cross: KkDd X KkDd

Progeny phenotypes:

9 = K_D_ = White petals

3 = kkD_ = White petals

3 = K_dd = Blue petals

1 = kkdd = White petals

Phenotypic ratio = 13:3

It is an example of dominant suppression epistasis.

It exhibits complete dominance at both gene pairs. However, the presence of a dominant allele at the upstream locus inhibits the effect of the downstream locus.

In the given case, K is downstream to D i.e. K is epistatic to D.

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