While doing fieldwork in Madagascar, you discover a new dragonfly species that has either red (R) or clear (r) wings. Initial crosses indicate that R is dominant to r. You perform three crosses using three different sets of red-winged parents with unknown genotype and observe the following data: Cross Phenotypes 1 72 red-winged, 24 clear-winged 2 12 red-winged 3 96 red-winged Which cross is likely to have at least one parent with the genotype RR?

Since R has been established to be dominant over r, in order for the outcome of a cross to yield 100% red-winged offspring as obtained in crosses 2 and 3, at least one of the parents must have RR as genotype. The other parent can have rr, RR or Rr genotype.

RR x rr

Progeny: all Rr genotype with red-winged phenotype

RR x RR

Progeny: all RR, red-winged

RR x Rr

progeny: RR, Rr, RR, Rr. All red-winged in appearance.

In order to produce clear wings (rr) as in cross 1, at least one r allele must be present in the genotype of the two parents, there cannot be RR genotype.

Hence, only crosses 2 and 3 requires at least one parent with RR genotype.