In a diploid organism, there are two characters: M and N. If an individual is heterozygous for character M and homozygous recessive for character N, how many different gamete genotypes can it produce? A. two, B. Two if the genes are linked, four if they are not, C. four if the genes are linked, two if they are not. D. four, E. two if the genes are linked, four if they are not, and four if crossing over occurs.