Hi there!

Question

I have this question for my bio/genetics homework, and I can't seem to figure it out.

It reads, "A true-breeding red snapdragon is crossed to a true-breeding white snapdragon. The F1 progeny are all red. When the F1 is selfed, the following F2 progeny are observed:

1850 red (55%)
670 pink (20%)
831 white (25%)
(3351 total)

Give the appropriate genotypes of the parents, F1 and F2 progeny and name the type of genetic interaction.

Additionally, if random mating were to happen between the gametes of the F2 generation, what phenotype classes would you expect in the resulting flowers?"

At first I thought it was incomplete dominance, but that wouldn't make sense of true Red was RR and true white was rr. Is there something I'm missing?

Answer 1

This is an example of recessive epistasis. The ratios are 9:3:4. Red flowers genotype would be R/-;W/-. Pink flowers would be r/r;W/- and white flowers would have either R/-;w/w or r/r;w/w. The f1 progeny being all red resembles one of the parents, which is a clue for epistasis. If it was incomplete dominance then a cross between RR and ww would result in all pink F1 generation. Hope this helps!