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Science · 2023 · 4 marks
CBSE 2023 · Region 6 · Set 1 · Q38
All human chromosomes are not paired. Most human chromosomes have a maternal and a paternal copy, and we have 22 such pairs. But one pair called the…
All human chromosomes are not paired. Most human chromosomes have a maternal and a paternal copy, and we have $\displaystyle 22$ such pairs. But one pair called the sex chromosomes, is odd in not always being a perfect pair. Women have a perfect pair of sex chromosomes. But men have a mismatched pair in which one is normal sized while the other is a short one.
(a)
In humans, how many chromosomes are present in a Zygote and in each gamete?
(b)
A few reptiles rely entirely on environmental cues for sex determination. Comment.
(c)
"The sex of a child is a matter of chance and none of the parents are considered to be responsible for it." Justify it through flow chart only.
OR
(c)
Why do all the gametes formed in human females have an X chromosome ?
Marking-scheme solution
(a) Zygote - $\displaystyle 23$ pairs / $\displaystyle 46$ chromosomes.
Gamete - $\displaystyle 23$ chromosomes.
(b) The temperature at which fertilised eggs are kept determines whether the animals developing in the eggs are male or female.
(c) Sex determination in Human beings
(c) The \(\displaystyle 23^{\text {rd }}\) pair or the sex chromosome in human females contains 'XX' chromosome. At the time of gamete formation, each gamete gets one X-chromosome.
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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.