CBSE 2022 · Region 1 · Set 2 · Q15

The mechanism by which the sex of an individual is determined is called sex-determination. In human beings, sex of a newborn is genetically determined, whereas in some others it is not. There are $\displaystyle 46$ ($\displaystyle 23$ pairs) chromosomes in human beings. Out of these, $\displaystyle 44$ ($\displaystyle 22$ pairs) control the body characters and $\displaystyle 2$ (one pair) are known as sex chromosomes. The sex chromosomes are of two types - X chromosome and Y chromosome. At the time of fertilisation, depending upon which type of male gamete fuses with the female gamete, the sex of the newborn child is decided.

(a)

Why is a pair of sex chromosomes in human beings called a mismatched pair in terms of type and size ? $\displaystyle \frac{1}{2}+\frac{1}{2}$

(b)

If the gametes always have half the number of chromosomes, then how is the original number of chromosomes restored in the organism ?

(c)

(i)OR(ii)

Name two animals whose sex is not genetically determined. Explain the process of their sex determination.

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