Question

In humans, a hypothetical trait is under the control of a single gene, A.  Four alleles have been found:  A1, which is dominant to all others;  A2, which is dominant to A3and A4, which are codominant. 

A) If gene A is on an autosome, how many different genotypes are possible?

B) If gene A is on an autosome, how many different phenotypes are possible?

C) If gene A is on the X, how many different genotypes are possible?

D) If gene A is on the X and homozygous and hemizygous genotypes have different phenotypes, how many different phenotypes are possible?

Answer 1

A) A1 A2, A1 A3, A1 A4
B) only one, as A1 is dominant over all others.