Question

How is the sex of a child fixed during the fertilization step in human beings? Explain. (3 marks)

Answer 1

Male produces two types of sperms. They are sperms carrying X chromosome and sperms carrying Y chromosome. Hence, human males are heterogametic. 

Females produce always an egg containing X chromosome. Hence, female is homogametic. 

When an sperm carrying X chromosome fuses with egg, this results in XX which will be a female. 
When an sperm carrying Y chromosome fuses with egg, this results in XY which will be a male. 

Sex of a child is determined at the time of fertilization.

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Answer 2

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Answer:

=> In the XY sex-determination system, the female-provided ovum contributes an X chromosome and the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in females (XX) or males (XY) offspring respectively. Hormones levels in the male parent affect the sex ratio of sperm in humans.

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