Drosophila melanogaster has one pair of sex chromosomes (XX or XY) and three pai

Question

Drosophila melanogaster has one pair of sex chromosomes (XX or XY) and three pairs of autosomes, referred to as chromosomes II, III, and IV. A genetics student discovered a male fly with very short (sh) legs. Using this male, the student was able to establish a pure breeding stock of this mutant and found that it was recessive. She then incorporated the mutant into a stock containing the recessive gene black (b, body color located on chromosome II) and the recessive gene pink (p, eye color located on chromosome III). A female from the homozygous black, pink, short stock was then mated to a wild-type male. The F_1 males of this cross were all wild type and were then backcrossed to the homozygous b, p, sh females. The F_2 results appeared as shown in the following table. No other phenotypes were observed. Based on these results, the student was able to assign short to a linkage group (a chromosome). Which one was it? X chromosome chromosome II chromosome III chromosome IV

Explanation / Answer

It is chromosome IV. Because if the 'short' gene would have been X linked then male Drosophila having only one X chromosome and Wild type would have had 'Sh' gene. So when the crosses would have taken place between male and female, all the males would have acquired recessive 'sh' gene because of XshXshX XShY =XshY (recessive), and based on the results we should have all the females dominant (wild type).

So now as we have three genes, the Short legs gene is located on chromosome no. IV

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