genetic cross dominance

hi i have a question: a genetic cross between two plants with yellow flowers produce a progeny of 80 plants, 38 of wich have yellow flowers, 22 red flowers and 20 white flowers. what kind of relationship between the alleles is present?
a) co-dominance
b) complete dominance
c) multiple alleles
d) incomplete dominance
e) epistasi
the answer is D but i think is A, can someone explain it to me please?

hi :slight_smile: I would actually say that the answer here is c) multiple alleles.

With co-dominance this would imply that the flowers would have a mixture of two different colours in one (for example, a flower with both yellow and red patches). But here, the final flowers are whole colours, meaning each flower only has one colour, so it can’t be co-dominance.

It also can’t be incomplete dominance because incomplete dominance is when two different colours mix to make one whole colour, so for example one yellow parent and one red parent flower would make orange flowers, which is a mix of yellow and red (but this is one COMPLETE colour, so there are no different coloured patches on it unlike in co-dominance). But this isn’t the case here either, because yellow, red and white aren’t mixtures of each other.

So I would say that the relationship between them is multiple alleles, because they all express different forms of the gene for colour.


I agreed with Francesca on the reason for this not being co-dominance but I believe the answer is D.

The ratio of progeny is approximately at 2:1:1 ratio as in the ratio of the genotypes in the cross between 2 heterozygous parents. (Aa x Aa → 1/4 AA, 1/2 Aa and 1/4 aa) → Yellow flowers have Aa genotype in this case.