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Science · 2022 · 4 marks
CBSE 2022 · Region 1 · Set 1 · Q14
The mechanism by which the sex of an individual is determined is called sex-determination. In human beings, sex of a newborn is genetically…
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)
Out of male or female, which of them has a perfect pair of sex chromosomes? In case of a perfect pair, will the gametes produced be of the same kind or of a different kind?
(c)
(i)
Name two animals whose sex is not genetically determined. Explain the process of their sex determination.
OR
(ii)
With the help of a flowchart only, show how sex is genetically determined in human beings.
Marking-scheme solution
XY
Y is shorter than X
(b)
Mother/Female
Same kind
(c) i) • Reptiles & Snails
In reptiles, the temperature at which fertilised eggs are kept determines whether the animal developing in the eggs would be a male or a female. In snails, they can change their sex during their life time.
OR
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CBSE Class 10 Science past-paper question from the 2022 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.