When a female fruit fly with notched wings is mated to a male with wild type rou

Question

When a female fruit fly with notched wings is mated to a male with wild type rounded wings, all the F1 offspring have notched wings. When a male with notched wings is mated to a female with wild type rounded wings all of the male offspring have wild type rounded wings and all of the female offspring have notched wings. You can assume that the Parent male and females are true-breeding (none of the parent flies are heterozygous).

a. Explain the observed pattern of inheritance. Specifically, state whether the notched wing trait is dominant or recessive and whether it is X-linked or on an autosome.

b. Again, using the format for Drosophila genes, assign genotypes to the two parent crosses and their F1 offspring.

Cross 1 notched wing females x rounded wing males: F1 offspring:

Cross 2 notched wing males x rounded wing females: F1 offspring:

c. What F2 phenotypes and ratios are expected if the F1 offspring of Cross 1 are mated with each other? Show your work.

Explanation / Answer

a. Notched wing is X-linked dominant.

b. Suppose XN = Allele for notched wing

and X = Allele for wild type wing

1. XNXN (female, notched) x XY (male, wild) will produce XXN females and XNY males in F1 progeny. Since XN is dominant, all the progenies will have notched wings.

2. XNY (male, notched) x XX (female, wild) will produce XY males and XNX females in F1. In this case, all the males progenies will have wild type wings and all the females will have notched wings.

c. 1. F2 progeny of Cross 1:

Since in the F1 progeny, all the females have XXN and males have XNY genotype; the progenies in F2 will be of XXN (female, notched) : XNXN (female, notched) : XY (male, wild) : XNY (male, notched) in the ratio of 1:1:1:1. The ratio of notched wing : wild type will be 3:1 in F2.

2. F2 progeny of Cross 2:

Since in the F1 progeny, all the females have XXN and males have XY genotype; the progenies in F2 will be of XX (female, wild) : XXN (female, notched) : XY (male, wild) : XNY (male, notched) in the ratio of 1:1:1:1. Half of the males and females will have noched wings.

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