Passage V

Chickens can have different types of combs (red crests on the top of the head). Two unlinked genes that influence comb type in chickens are Gene R and Gene P. Table 1 lists 4 comb types in chickens and gives the Gene R and Gene P genotype(s) responsible for each comb type. In the genotypes, capital letters indicate dominant alleles and lowercase letters indicate recessive alleles.

Several chickens with the genotype Rrpp were crossed with chickens having the genotype rrPp. The percent of the resulting offspring having each comb type is shown in Table 2.