Problem:

In Drosophila, the X-linked eye colors are tinged, ivory, eosin, apricot, wine and blood are caused by a series of 6 alleles all of which are recessive to the seventh wildtype allele red, but which produce intermediate phenotypes in all other heterozygotes. In other words, females heterozygous for the allele determining red have red eyes, but females heterozygous for the alleles determining tinged and ivory have an eye color that is intermediate to these two colors.

Question 1: How many different hemizygous genotypes exist?
(a) six
(b) seven
(c) twelve
(d) fourteen
(e) twenty one

Please explain your reasonings