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.

A) Explain what is going on genetically

B) why short bristled females can not be homozygous.

Please correct answer. Thanks

Explanation / Answer

A. This is X linked inheritance. Also XAY is lethal.

The first cross XAXa X XaY

1 XAXa - Short bristled females
1 XaXa - Long bristled female
1 XaY - Long bristled male
1 XAY - Non viable males

2. Long bristled female XaXa X XaY - Long bristled male

XaXa Long bristled female and XaY Long bristled male

B. It cant be homozygous XAXA X XaY
XAXa and XAY only two possibilites are possible.

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