A virgin Drosophila female whose thorax bristles are very short is mated with a

Question

A virgin Drosophila female whose thorax bristles are very short is mated with a males having normal (long) bristles. The F1 progeny are 1/3 short-bristle females, 1/3 long bristle females, and 1/3 long bristle males. A cross of the F1 long bristle females with their brothers gives only long bristle F2 progeny. A cross of short bristle females with their brothers gave 1/3 long bristle females, 1/3 short bristle females, and 1/3 long bristle males. Explain what is going on genetically.

Please show how you got the answer. Thank you

Explanation / Answer

I assume that you have forgot to mention if the gene is recessive lethal; therefore, that's why the ratios don't exactly up.

Now if i think the trait is autosomal, then it should be distributed equally to all offspring irresepctive of whether or not they are male or female. It is a sex-linked trait then the ratios are different for male vs. female.

In first F1, no males get short-bristles; whereas in scond cross two, short and long bristles are equally distributed across males and females. So i conclude that the ratios are evenly distributed, it's autosomal. If the ratios are different between male and female, it's sex-linked.

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