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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 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 ?How is the original number of chromosomes present in the parents restored in the progeny ?Explain by giving two examples of the organisms in which the sex is not genetically determined.
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 ?
How is the original number of chromosomes present in the parents restored in the progeny ?
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)
Example $\displaystyle 2$ : Snails - Individuals can change sex during their lifetime.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.
OR
(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.
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CBSE Class 10 Science past-paper question from the 2023board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.