If you have ttRR x TTrr on a punnet square, what is the mode of inheritance expressed?

Question

a)dominance in both pairs of genes
b)codominance in both pairs of genes
c)codominance in one pair of genes
d)multiple alleles

Answer 1

Your answer would be:
a) dominance in both pairs of genes

This is because, even though the cross is ttRR x TTrr, nothing is said about how the genes are expressed, so we assume regular Mendelian genetics. So, the T allele is dominant over the t allele, and the R is dominant over the r. Codominance is when neither allele is dominant overe the other and the phenotype includes the phenotypes of both of the parents.

I know dominance, incomplete dominance, and codominance are tricky, it took me a while to get it. But an example of codominance is blood type, because people can be AB, right? So, the A came from one parent and the B came from another...neither is dominant. Both are expressed.

Answer 2

b, codominance in both pairs of genes

100% offspring TtRr