Q1. [1]
When a sperm carrying the Y chromosome fertilises an egg, the resulting zygote would have the following combination of chromosomes :
- (a) 44 + XX
- (b) 44 + XY
- (c) 22 + XX
- (d) 22 + XY
Previously asked in CBSE board exam
2023 31/2/1 Q12
Generated by claude-sonnet-4-6 · 2026-06-15 06:52 · grounding rag
Model Answer
(b) 44 + XY
When a Y-carrying sperm fertilises an egg (which carries X), the zygote has 44 autosomes + XY sex chromosomes.
Source: What you have learnt, Chapter 8
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Explanation
- Every human egg carries 22 autosomes + X; every sperm carries 22 autosomes + X or Y.
- At fertilisation, both sets combine: 22 + 22 = 44 autosomes, and X (egg) + Y (sperm) = XY.
- Total = 44 + XY → male offspring.
- Common mistake: choosing 22 + XY (forgetting that fertilisation doubles the chromosome number from each gamete).
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