The correct option is C Starch synthesis in pea : Multiple alleles
Starch synthesis in pea plants is controlled by a single gene that has two alleles - B and b. The BB homozygotes can produce starch more effectively and thus large starch grains are produced which are round at maturity. The bb homozygotes can produce starch less effectively and thus produce small sized starch grains which are wrinkled at maturity. The Bb heterozygotes are of intermediate size and round at maturity. When the size of the seed is considered, the alleles show incomplete dominance.
AB blood group is an example of codominance as alleles for A and B antigens gets expressed simultaneously in heterozygous individuals.
Grasshopper is an example of XO type of sex determination in which the males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes.
T.H. Morgan studied linkage of genes in Drosophila.