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Science · 2023 · 4 marks
CBSE 2023 · Region 5 · Set 1 · Q38
In some families, either rural or urban, females are tortured for giving birth to a female child. They do not seem to understand the scientific…
In some families, either rural or urban, females are tortured for giving birth to a female child. They do not seem to understand the scientific reason behind the birth of a boy or a girl. In fact the mother is not responsible for the sex of the child and it has been genetically proved that the sex of a newborn is determined by what the child inherits from the father.
(a)
State the basis on which the sex of a newborn baby is determined in humans.
(b)
Why is the pair of sex chromosomes called a mismatched pair in males ?
(c)
How is the original number of chromosomes present in the parents restored in the progeny ?
OR
(c)
Explain by giving two examples of the organisms in which the sex is not genetically determined.
Marking-scheme solution
(a) If X chromosome of male sperm fuses with X chromosome of female ova, girl child is born. If Y chromosome of male sperm fuses with X chromosome of female ova, boy child is born.
Alternate answer:
(b) Because one is a normal sized 'X' while the other is a short one 'Y'.
(c)
During formation of germ cell/gametes the chromosome number is reduced to half.
When two germ cells from two individuals combine to form a new individual, they restore the original number of chromosomes.
(c) Example $\displaystyle 1$ : Reptiles - The temperature at which fertilized eggs are kept determines whether the animals developing in the eggs will be male or female.
Example $\displaystyle 2$ : Snails - Individuals can change sex during their lifetime.
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CBSE Class 10 Science past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.