Q7 of 13 Page 159

Babu heard his mother and aunty talking about his cousin who is going to have a baby; they were discussing whether she would give birth to a boy or girl,

a. Will it be possible to judge the sex of the child by them?


b. What makes the fertilized egg develop either into a boy or a girl?

A. No, it is not possible to judge the sex of the child because there are only 50% chances that the baby could be a boy the other 50% chances says that the baby could be a girl also!


B. The total number of chromosome in human body is 46. During the period of gamete formation, this number gets reduced to half i.e. 23 chromosomes. 22 chromosomes are similar in males and females. These 22 chromosomes are known as autosomes. The 23rd chromosome is known as the sex chromosome as it determines the sex of the human. Females have ‘XX’ chromosome, while, males have ‘XY’ chromosome.


When a sperm containing ‘X’ chromosome fertilizes the egg, the zygote will have ‘XX’ chromosome and the egg develops into a girl.


When a sperm containing ‘Y’ chromosome fertilizes the egg, the zygote will have ‘XY’ chromosome and the egg will develop into a boy.


Diagram showing(A). 23 pair of chromosomes in humans.


(B). Sex determination in humans through chromosome


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