Question

HELP!! I still don't understand the concepts of "Incomplete dominance" and "co-dominance" D; This question: In chickens, the frizzle gene “F” controls the appearance of the feathers. A homozygous dominant chicken for the frizzle gene shows “extreme frizzle”, that is his feathers are extremely disrupted. The normal chicken is homozygous recessive and has undisrupted feathers. When a chicken with extreme frizzle is mated with a normal chicken, all of the offspring exhibit mild frizzle.

Answer 1

a. Is the mode of inheritance incomplete dominance or co-dominance? Why?
b. What would you expect to see if the mode of inheritance was the other alternative in part (a)?
c. Show the expected phenotypic and genotypic ratios if two chickens with mild frizzle are mated.

Answer 2

Incomplete dominance is when two alleles are equally dominant, they interact to produce a new phenotype. And co-dominance is when both alleles are expressed at the same time.

For instance, incomplete dominance: red-flowering and white-flowering snapdragons combine to produce pink-flowering plants.

Co-dominance: A red bull crossed with a white cow produces a roan calf. The roan calf has intermingled white and red hair.

Therefore, is the problem co-dominance instead of incomplete dominance?

Answer 3

Or still incomplete dominance since 'mild frizzle' is a new phenotype? The problem says "all of the offspring exhibit mild frizzle" and that reminds me of the snapdragons where the red and white flower produced pink...

Answer 4

I agree with your statement about the 'mild frizzle' telling us that it is incomplete.
We don't see patches of 'extreme frizzle' and 'normal'. The two mix, not display separately.