A cross is made between two pure breeding cattle breeds, where one breed is resistant to a tick species due only to a dominant allele of a gene for resistance, and the other breed is resistant only due to a recessive allele at a different gene to the first for resistance. Both genes are autosomal. The F1 between the breeds was resistant; what is the expected ratio of resistant to susceptible cattle in the F2 generation assuming independent assortment of the two autosomal genes? (Hint:
once a cattle individual is resistant because of its genotype at one of the genes, having resistance determined by the other gene does not give increased resistance, i.e. there are only 2 phenotypes: resistant and susceptible)
Select one of the following: