Question

Explain sex determination in humans with the help of a flow- chart.

Answer 1

Hint: Among the 23 pairs of chromosomes, the 23rd pair are sex chromosomes (which determine whether the offspring will be male or female), XX for females, or XY for males. They participate in sex determination.

Complete answer:
In a human being, the sex of a child is determined depending upon which type of male gamete fertilizes with the female gamete. There are 23 pairs of chromosomes in each of the mother and the father. Out of 23 pairs, 22 pairs are said to be autosomes and one pair is called sex chromosomes (in male XY and female XX). At the time of fertilization, the sperm fertilizes the egg cell to form the zygote. If the sperm carrying X- chromosome fertilizes an ovum carrying an X chromosome, then the child born will be a girl. If the sperm carrying Y- chromosome fertilizes an ovum carrying X- chromosome, the child born will be a boy.

Figure: Sex determination


Additional Information:
- Sex is the hereditary difference between two individuals of the same species.
- X- chromosomes were first identified by Wilson and Stevens in 1905.
- Autosomes are chromosomes that are the same in both types of sexes.
- Sex chromosomes are also known as allosomes.
- Males are known as heterogametic because they possess the Y- chromosome.
- Two short arms (p arms), two longer arms (q arms), and a centromere at the center are present in each chromosome.

Note:
- At the time of spermatogenesis, there will be two types of sperm cells produced in equal numbers, one containing an X- chromosome and the other containing a Y chromosome.
- Since in males, one sex chromosome is X and the other is Y, they are called heterogametic while the females are homogametic because of two X chromosomes.