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 mismatch 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.
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 mismatch 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.
(a) In human males, the sex chromosomes are called a mismatched pair because they consist of one normal-sized chromosome and one shorter chromosome, unlike the other 22 pairs which are perfect matches.
(b) Females have a perfect pair of sex chromosomes (). Since they have two chromosomes, all gametes (eggs) produced by a female will be of the same kind, each carrying one chromosome.
(c) (i) Two animals whose sex is not genetically determined are:
- Reptiles (e.g., some lizards/turtles): The temperature at which fertilized eggs are kept determines whether the developing animal will be male or female.
- Snails: In snails, individuals can change sex, indicating that sex is not fixed by genes at birth.
OR
(ii) Flowchart for Sex Determination in Humans:
``mermaid
graph TD
P1[Father XY] -- Gametes --> G1[X]
P1 -- Gametes --> G2[Y]
P2[Mother XX] -- Gametes --> G3[X]
P2 -- Gametes --> G4[X]
G1 -- "Fertilisation" --> C1[XX Female Child]
G2 -- "Fertilisation" --> C2[XY Male Child]
G3 -- "Fertilisation" --> C1
G4 -- "Fertilisation" --> C2
``
Marking Scheme
- 1Explanation of mismatched pair (size and type) (1 mark)
- 2Identification of perfect pair (Female) and gamete type (1 mark)
- 3Non-genetic examples (Reptiles/Snails) and explanation (2 marks)
- 4OR Flowchart showing XY and XX cross (2 marks)
Hint
Remember that the mother always contributes an chromosome; the father's sperm determines the sex.
Quick Oral Answer
Sex in humans is determined by the sex chromosomes. Females have and males have . The father determines the sex because he can provide either an or a chromosome to the offspring. In some animals like snails, sex can change during their lifetime.
Analysis & Explanation
In humans, sex is determined genetically by the father's contribution. Females are homogametic (), meaning they produce only one type of gamete (). Males are heterogametic (), producing two types of gametes ( and ). If a sperm carrying an chromosome fertilizes the egg, the child is a girl (). If a sperm carrying a chromosome fertilizes the egg, the child is a boy (). This results in a probability for either sex. In contrast, environmental factors like temperature or social changes (as in snails) can determine sex in other species.
Common Mistakes
- 1Thinking that the mother determines the sex of the child.
- 2Confusing the number of pairs (23) with the total number of chromosomes (46).
Interesting Facts
In some reptiles, higher temperatures produce males, while in others, they produce females.
The Y chromosome is significantly smaller than the X chromosome in humans.
Spotted a mistake or something unclear?
Tell us — we fix reported answers fast.
Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2022?
This question carries 4 marks in the CBSE Class 10 Science 2022 examination.
Which chapter does this question come from in Science?
This question is from the chapter "Heredity" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Sex Determination" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2022 paper?
This question appears in Section C in the CBSE Class 10 Science 2022 paper.