Question

PROBLEM ANIMAL GENETIC CROSSING I 1. In the fruit fly Drosophiliamelanoganster, wings (A) are dominant over a lack of wings (a) and red eyes (E) are dominant over brownish eyes (e). A wingless fly that is heterogynous for eye colour is crossed with a fly that is heterozygous for both eye colour and presence of wings. From your cross 1. What is the genotypic and phenotypic ratios for this cross? 2. What fraction of the offspring from this cross will be wingless and have brownish eyes? 3. What fraction will have AaEe 2. You have a winged red-eyed fruit fly. Design the cross to determine whether the fly is heterozygous for either or both traits. Use a punnet square to show all possible crosses.​

Answer 1

1. Genotypic and Phenotypic Ratios for the Cross:

• Genotypic ratio: AaEe : AaEE : aaEe : aaEE
• Phenotypic ratio: Winged red eyes : Winged brownish eyes : Wingless red eyes : Wingless brownish eyes

1. Fraction of Offspring with Wingless and Brownish Eyes:

To determine the fraction of offspring with wingless and brownish eyes, we need to look at the aaee genotype, as it represents the wingless and brownish eye combination. From the Punnett square, we find that 1/4 of the offspring will have the aaee genotype.

2. Fraction of Offspring with AaEe:

To find the fraction of offspring with the AaEe genotype, we need to look at the Punnett square and count the number of offspring with this genotype. From the Punnett square, we find that 2/4 (or 1/2) of the offspring will have the AaEe genotype.

For the second part of the question:

To determine whether the winged red-eyed fruit fly is heterozygous for either or both traits, we can perform a test cross. We need to cross the winged red-eyed fly with a fly that is homozygous recessive for both traits (aaee genotype). Then, we can observe the phenotypes of the offspring to infer the genotype of the winged red-eyed fly.

Punnett Square for Test Cross:

AaEe AaEe

aaee Aaee Aaee

aaee Aaee Aaee

If any of the offspring show the wingless and brownish eye phenotype (aaee), it means the winged red-eyed fly is heterozygous for both traits (AaEe). If none of the offspring show the aaee phenotype, it means the winged red-eyed fly is heterozygous for either the wing trait (AaEE) or the eye color trait (aaEe).