Question

Answer the following questions related to sex determination in human beings:
What is a sex chromosome?
How many pairs of chromosomes are there in human beings?
How is the sex of the human offspring determined?
Draw a diagram depicting sex determination in man.

Answer 1

Hint: Most organisms including humans produce their offspring by the means of sexual reproduction involving the fusion of male and female gametes. Sex determination is a system that helps to determine the development of sexual characteristics in an organism. The sex is determined after fertilisation.

Complete answer:
The chromosomes are the thread-like structure present in the nucleus. A chromosome is made up of DNA which is transmitted from parent to offspring. They are of two types, autosomes and sex chromosomes.
a) The autosomes are present in the body or somatic cells. They have a vegetative role.
b) Sex chromosomes- Sex chromosomes are the chromosomes that help in the determination of sex. These chromosomes are present in the reproductive cells that are eggs in female and sperm in male. In humans, there are two sex chromosomes X and Y.
(ii) human beings have 23 pair of chromosomes. It includes 22 pair of autosomes and one pair of sex chromosome. The chromosomes of males are represented as 22 +XY, and females as 22 + XX.
(iii) The determination of sex is carried out by the sex chromosomes. The sex of a human being is determined at the time of fertilisation. The XY chromosome of the male is crossed with the XX of a female.
The gametes formed are X, Y of male and X of female. The cross is represented as follows

	X	Y
X	XX (Female)	XY (male)

Hence the possibility of the male and female offspring produced is 1:1.
(IV) The diagram showing the fusion of gametes and the formation of offsprings.

Note: Karyotyping is the method of pairing and order the chromosomes in an organism. It helps in providing the genome of an individual chromosome. At times instead of 46 chromosomes 47 chromosomes can exist. For example, 44+XYY- these are called super males. It is a rare disorder in male. Like-wise super females have a triple X chromosome.