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What chromosome combinations produce XX and XY human zygotes?
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Fertilization
Fertilization occurs when a sperm cell penetrates and fuses with an egg (ovum).
In humans, the sex of a zygote is determined at the moment of fertilization by the combination of sex chromosomes contributed by the egg and the sperm.12
Because human females possess two X chromosomes, all normal egg cells carry a single X chromosome. Human males possess an XY chromosome pair, meaning that during meiosis, sperm cells receive either an X or a Y chromosome in equal proportions.134
The resulting zygote combinations are as follows:
- XX (Female): Produced when an egg (carrying an X chromosome) is fertilized by a sperm carrying an X chromosome.134
- XY (Male): Produced when an egg (carrying an X chromosome) is fertilized by a sperm carrying a Y chromosome.134
This chromosomal constitution is the primary factor in sex determination, with the presence of the Y chromosome typically stimulating the development of male anatomical structures.12