Principle of Inheritance and VariationEasyBloom L2
Question
In Drosophila, the sex is determined by
Options
A.The ratio of number of XX-chromosomes to the sets of autosomes
B.X and Y chromosomes
C.The ratio of pairs of X-chromosomes to the pairs of autosomes
D.Whether the egg is fertilized or develops parthenogenetically
Solution
(b) [Key Concept: Sex Determination in Drosophila — X:A Ratio] In Drosophila, sex is determined by the RATIO of the NUMBER of X-chromosomes to the SETS of AUTOSOMES (X:A ratio). This was demonstrated by Calvin Bridges. X:A = 1.0 → female; X:A = 0.5 → male; X:A = 0.67 → intersex. The Y chromosome is NOT sex-determining in Drosophila (XO flies are males, not females). This differs from humans where the Y chromosome (SRY gene) is the primary sex determinant.
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