A female Drosophila with the mutant phenotype a is crossed to a male who has the

Question

A female Drosophila with the mutant phenotype a is crossed to a male who has the mutant phenotype b. In the resulting F1 generation all females are wild-type and all males have the a mutant phenotype. Based on these results, we can conclude that the mode of inheritance of the phenotype of interest is: A) autosomal for a and X-Linked for b B) dominant for a and recessive for b C) recessive for a and dominant for b D) recessive for both a and b E) X-linked for a and autosomal for B

The correct answer is D. Can someone explain why?
A female Drosophila with the mutant phenotype a is crossed to a male who has the mutant phenotype b. In the resulting F1 generation all females are wild-type and all males have the a mutant phenotype. Based on these results, we can conclude that the mode of inheritance of the phenotype of interest is: A) autosomal for a and X-Linked for b B) dominant for a and recessive for b C) recessive for a and dominant for b D) recessive for both a and b E) X-linked for a and autosomal for B

The correct answer is D. Can someone explain why?
A) autosomal for a and X-Linked for b B) dominant for a and recessive for b C) recessive for a and dominant for b D) recessive for both a and b E) X-linked for a and autosomal for B

The correct answer is D. Can someone explain why?

Explanation / Answer

This is an example of X-linked recessive inheritance.

This is caused by mutation of genes on X-chromosome. Since females carry 2 X-chromosomes, one from each parent, there is less chance for a female to carry mutant copies of genes on both X-chromosomes.

Since males have only one X-chromosomes, received from the female parent, one altered gene is enough to cause mutant phenotype. All males have 'a' mutant phenotype because the male parent cannot transfer X-linked traits to progeny.

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