Science
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 46 (23 pairs) chromosomes in human beings. Out of these, 44 (22 pairs) control the body characters and 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 ?
(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.
Genetics
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Answer
(a) A pair of sex chromosomes in human beings is called a mismatched pair in terms of type and size because in males one chromosome is a normal-sized X while the other is a short one called Y. Such a pair of chromosome is known as heteromorphic.
(b) Female has a perfect pair of sex chromosomes. Since all chromosomes are alike, the gametes produced are of same kind.
(c) (i) The two animals whose sex is not genetically determined are Snail and Green Sea Turtle.
- Green Sea Turtle — Green Sea Turtle exhibits temperature-dependent sex determination. Temperature at which the eggs are incubated determines the sex of the offsprings. Cooler temperatures (around 29°C) result in the development of male hatchlings, while warmer temperatures (around 33°C) lead to the development of female hatchlings.
- Snail — In snails, individuals can change sex, indicating that sex is not genetically determined. The snail is born as a male but eventually changes into a female. Snails use physical contact with other snails to guide sex change.
OR
Below flowchart shows genetic sex determination in human beings:
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