Q92 - Deducing an X-Chromosome Deletion from an Unusual Drosophila Cross

Theoretical B Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Chromosomal Variation: Number & Structure

A wildtype female Drosophila was mated with a wildtype male that had been X-ray irradiated. One of the F1 females was mated with a male that had recessive phenotype (caused by recessive allele a). Progenies of the second mating were unusual in two aspects. Firstly, there were twice as many females as males. Secondly, while all the males were wild type, 1/2 of the females were wild type, and the other 1/2 exhibited the recessive phenotype a.

Indicate in the answer sheet if each of the following statements is true or false.

Using the information and data, determine which of the statements are true or which are false.

A. X-rays converted a dominant allele (A) on the chromosome X, coding for wild type, to a recessive allele (a).

B. X-rays produced a chromosomal translocation.

C. A loop might be seen on one pair of chromosomes during prophase of meiosis 1 in the mated F1 female.

D. If a female from the second mating exhibiting recessive phenotype (a) was crossed to a wild type male then her progenies compose of females and males at the ratio of 2 females to 1 male.

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Question reproduced from IBO 2016, Theoretical Paper B, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)