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Principles of Inheritance and Variation
Sex Determination: Genic Balance
1 question from 1 paper, each with its answer.
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Concepts tested
- X to autosome ratio in Drosophila
All Questions
2003 AIPMT 1 question
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In Drosophila, the sex is determined by : -In Drosophila, sex is determined by the genic balance mechanism proposed by C. B. Bridges.
Sex depends on the ratio of the number of X chromosomes (X) to the number of sets of autosomes (A), i.e. the X/A ratio. The Y chromosome does not decide sex (it is needed only for male fertility).
X/A = 1 (e.g. XX + 2A): female. X/A = 0.5 (e.g. XY + 2A): male. X/A between 0.5 and 1: intersex. X/A greater than 1: metafemale; less than 0.5: metamale.
Determination by fertilised or unfertilised egg (haplodiploidy) occurs in honeybees.
So in Drosophila, sex is determined by the ratio of the number of X chromosomes to the sets of autosomes.