Biology Notes on Sex Determination in Human Beings for SSC Exam

In this article, we will discuss the sex determination in human beings. This is an important topic in biology and questions are frequently asked from this topic.

Sex Determination:

• In a human being, we determine the sex with the help of the sex chromosome i.e. with the help of X and Y chromosome.
• In a human being, 46 chromosomes are found out of which 44 are found in 22 pairs called autosomes and the other two chromosomes are called sex chromosomes.
• The rest two chromosomes are the same in females and are called X- chromosomes (XX).
• In a male, the rest two chromosomes are different and are called X and Y chromosomes.
• During reproduction females produce one type of gametes and containing 22 autosomes and one X chromosomes, while males produce two types of gametes one have 22 + X type chromosomes and others have 22+ Y types of chromosomes.
• When male gametes i.e. sperm carrying X chromosomes fertilizes an ova, the zygote develops into a female.
• When a sperm carrying Y chromosomes fertilizes an egg, Zygote develops into a male.

Some Genetic Disorder occurs due to Chromosomes:

Klinefelter Syndrome:

• When a male has an extra X or Y chromosome in sex chromosomes then the condition will be XXY or XYY instead of XY. The individual became sterile in this condition.
• In female when an extra X chromosome is present instead of XY they show normal development but limited fertility, metal retardness is also seen in this type of syndrome.

Turner’s Syndrome:

• When female has single-sex chromosome (X0) their ovaries are rudimentary, lack of secondary sexual characteristics.

Down’s Syndrome:

When an extra chromosome is added to 21^st autosomal chromosomes this lead to develop Down’s syndrome.

Colour Blindness:

• This disorder leads to failure to distinguish between red & green colour.
• The gene responsible for this disease is situated on sex chromosomes.

Patau’s Syndrome:

• This type of syndrome is developed by addition of autosomal chromosome in 13^th chromosome.
• There is a cut mark in the lip and the person is mentally retarded.

Number of Chromosomes in Different Organisms:

S. No.	Organisms	No. of Chromosomes
1.	Pigeon	80
2.	Dog	78
3.	Horse	64
4.	Chimpanzee	48
5.	Human	46
6.	Rabbit	44
7.	Cat	38
8.	Frog	26
9.	Pea	14
10.	Tomato	24
11.	Wheat	42
12.	Potato	48

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