A fruit fly with a diploid set of autosomes has one X chromosome but no Y chromosome. This fly would be

Question

BlackTom AI · Accepted Answer

Drosophila sex is determined by the ratio of X chromosomes to sets of autosomes (X:A ratio), not simply by the presence or absence of a Y chromosome.

1) Relevant concepts
- X:A ratio rule in Drosophila: X chromosome number divided by the number of haploid sets of autosomes determines sexual phenotype. A ratio of 1.0 (for example XX with two sets of autosomes) produces a female; a ratio of 0.5 (for example X0 or XY with two autosome sets) produces a male. Intermediate ratios (e.g., 0.67) produce intersex phenotypes. The Y chromosome is not required for male determination but is required for male fertility.

2) Step-by-step reasoning
- Determine X count: 1 (one X chromosome).
- Determine autosomal sets: diploid autosomes means two sets (A = 2).
- Compute X:A ratio: X/A = 1 / 2.

3) Calculations (intermediate steps)
- X = 1
- A = 2
- X:A = 1 ÷ 2 = 0.5

4) Why this yields the correct answer
- An X:A ratio of 0.5 corresponds to the male developmental pathway in Drosophila. Thus a fly with one X and no Y (X0) will develop as a phenotypic male. However, because the Y chromosome carries genes required for spermatogenesis, an X0 male is typically sterile.

5) Why the other options are incorrect
- "A female.": Incorrect because a female requires an X:A ratio of ~1.0 (e.g., XX with two autosome sets). One X with two autosome sets gives 0.5, not 1.0.
- "A hermaphrodite.": Incorrect because hermaphroditism is not the Drosophila outcome for an X:A ratio of 0.5; intermediate ratios produce intersex, but 0.5 produces a male phenotype.
- "Neither a male, nor female, nor hermaphrodite.": Incorrect because the X:A ratio clearly specifies a male phenotype (X0 → male), so the fly is not sexless.

6) Conclusion
- The fly would be a male. This matches the provided correct answer: "a male."

A fruit fly with a diploid set of autosomes has one X chromosome but no Y chromosome. This fly would be单项选择题

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