Discussion
Which among the following phenomena interfers with the balance theory of sex determination in Drosophila ?
Answer: B
The phenomenon is non-disjunction.
Bridges' genic balance theory says sex in Drosophila depends on the balance between X chromosomes and sets of autosomes. Non-disjunction, the failure of chromosomes to separate at meiosis, upsets that balance by producing gametes with extra or missing X chromosomes. The resulting flies, such as XXY females, XO males, and the intersexes and metafemales from triploid lines, change the X:A ratio and the sex that follows; studying them is how Bridges worked the theory out.
Linkage and crossing over rearrange alleles but do not change chromosome numbers, and sex in Drosophila is genetic, not environmental.
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