1 Each human cell contains 46 chromosomes or 23 pairs of chromosomes. 44 or 22 pairs of these chromosomes are known as autosomes.
2 The 23rd pair or the last two chromosomes are known as sex chromosomes.
3 There are two types of sex chromosomes which are the X chromosome or Y chromosome. These chromosomes determine the sex of a person. A human male will have one X and one Y chromosome, whereas a human female will have two X chromosomes.
4 The X chromosome is longer than the Y chromosome.
Sex Determination
1 The human male will have a genetic makeup (genotype) of 44 + XY, that is 22 pairs of autosomes and two types of sex chromosomes, X and Y.
2 The human female will have a genetic makeup of 44 + XX, that is 22 pairs of autosomes and one type of sex chromosome, XX.
3 Only the X and Y chromosomes play a role in determining the gender of the individual. The autosomes do not play any role in gender determination.
4 The sperm (male gamete) will carry either the Y chromosome or the X chromosome.
5 The ovum (female gamete) will carry only the X chromosome.
6 Figure 3.6 shows the production of male gametes or sperms in the testes through meiosis.
7 Figure 3.7 shows the production of female gametes or ova in the ovaries through meiosis.
8 During fertilization, a sperm will fertilize one ovum to produce a zygote.
9 If the sperm that carries the Y chromosome fuses with an ovum, the zygote formed will be a male.
10 However, if the sperm that carries the X chromosome fuses with the ovum, the zygote formed will be a female.
11 Figure 3.8 examines both of these possibilities.
12 The sex chromosome of the sperm of the father is responsible for determining the gender of the child.
13 Theoretically, the chance of getting a male child is 50% and a female child is also 50%.
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