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Exercises · Q11

Q.How is sex determined in human beings?

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Human sex is determined by the father's sperm, which carries either an X or a Y chromosome, combining with the mother's ovum, which always carries an X chromosome.

The determination of sex in human beings is a fascinating biological process rooted in our genetic makeup, specifically involving a special pair of chromosomes known as sex chromosomes. Understanding this mechanism requires a look at the fundamental units of heredity: chromosomes.

Every human cell typically contains 23 pairs of chromosomes, making a total of 46 chromosomes. Of these, 22 pairs are called autosomes, which carry genes for all other traits and are identical in both males and females. The 23rd pair, however, consists of the sex chromosomes, which are responsible for determining an individual's biological sex.

There are two types of sex chromosomes: the X chromosome and the Y chromosome.

  • Females possess two X chromosomes, denoted as XX.
  • Males possess one X chromosome and one Y chromosome, denoted as XY.

During the formation of gametes (sperm in males and ova in females), these chromosome pairs separate.

  • A female, having an XX genotype, can only produce ova that carry an X chromosome. All her eggs are genetically identical in terms of sex chromosomes.
  • A male, with an XY genotype, produces two types of sperm in roughly equal proportions: half of his sperm carry an X chromosome, and the other half carry a Y chromosome.

The sex of a child is determined at the moment of fertilization, when a sperm fuses with an ovum. Since all ova carry an X chromosome, the determining factor is the type of sperm that fertilizes the ovum:

  • If an X-carrying sperm fertilizes the ovum, the resulting zygote will have an XX combination, developing into a female child.
  • If a Y-carrying sperm fertilizes the ovum, the resulting zygote will have an XY combination, developing into a male child. …

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