Question

While doing field work 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 redwinged parents with unknown genotype and observe the following data:

cross Phenotype
1 72 red-winged,24 clear-winged
2 54 red-wing,49 clear-wing
3 96 red-winged

What is the most likely genotype for each pair of parents in the three crosses?

Answer 1

Answer: 1. The genotypes of parent that produced 72 red-winged,24 clear-winged are Rr and Rr.

2. The genotypes of parent that produced 54 red-wing,49 clear-wing are Rr and rr.

3. The genotypes of parent that produced 96 red-winged can either be RR and RR or RR and Rr.

Explanation: To get parent's genotypes from offspring's phenotypes, find the phenotypic ratio among the offsprings produced. That will give insight on the allele combination of the parent.

In the case where 72 red-winged,24 clear-winged were produced, the ratio will be 72:24. Dividing the ratio to the lowest term, we will get 3:1. This implies that the ratio of dominant to recessive alleles in the offspring genotypes is 3:1. Only heterozygous crossing can produce the ratio. We can then assign the parent's genotypes as Rr and Rr.

In the case where 54 red-wing,49 clear-wing were the offspring produced, the ratio will be 54:49. Dividing it to the lowest term, we will get approximately 1:1. This implies that the ratio between dominant and recessive allele is 1:1. A test cross will produce this ratio. We can then assign the parent's genotypes as Rr and rr.

In the cross that produced only 96 red-winged flies, the parent's genotypes can either be RR and Rr or RR and RR.