In human beings, there are 23 pairs of chromosomes. Out of these 23 pairs of chromosomes (i.e. 46 chromosomes), 22 pairs of chromosomes are called autosomes and one pair of chromosomes. i.e. two chromosomes are called sex chromosomes. The sex chromosomes are of two types - 'X' chromosomes and 'Y' chromosomes. The sex of a child (i.e. progeny), is decided at the time of fertilisation. In other words, at the time of zygote formation the sex chromosomes inherited from the parents of a child decide whether the new born will be a boy or a girl.
(a) What are chromosomes?
(b) Why is the pair of sex chromosomes in human males called mismatched pair?
(c) (A) Show with the help of a flow chart that the statistical probability of getting a boy or a girl is .
OR
(c) (B) Mention two examples of animals where sex is not determined genetically like human beings. Describe in brief the method of sex determination in these animals.
In human beings, there are 23 pairs of chromosomes. Out of these 23 pairs of chromosomes (i.e. 46 chromosomes), 22 pairs of chromosomes are called autosomes and one pair of chromosomes. i.e. two chromosomes are called sex chromosomes. The sex chromosomes are of two types - 'X' chromosomes and 'Y' chromosomes. The sex of a child (i.e. progeny), is decided at the time of fertilisation. In other words, at the time of zygote formation the sex chromosomes inherited from the parents of a child decide whether the new born will be a boy or a girl.
(a) What are chromosomes?
(b) Why is the pair of sex chromosomes in human males called mismatched pair?
(c) (A) Show with the help of a flow chart that the statistical probability of getting a boy or a girl is .
OR
(c) (B) Mention two examples of animals where sex is not determined genetically like human beings. Describe in brief the method of sex determination in these animals.
(a) Chromosomes are thread-like structures in which the genetic material (DNA) is tightly packed within the nucleus of a cell.
(b) The pair of sex chromosomes in human males is called a mismatched pair because they are not identical (one is X and the other is Y).
(c) (A) Flow chart to show the statistical probability of getting a boy or a girl is :
OR
(c) (B) Two examples of animals where sex is not determined genetically like human beings are:
- Earthworms: In earthworms, sex is determined by the presence or absence of a specific hormone. If the hormone is present, the earthworm develops as a male, and if it is absent, the earthworm develops as a female.
- Honeybees: In honeybees, sex is determined by the number of times the egg is fertilized. If the egg is fertilized once, it develops as a female (worker bee), and if it is fertilized twice, it develops as a male (drone).
Marking Scheme
- 14 marks
Common Mistakes
- 1confusing autosomes with sex chromosomes
- 2thinking that sex determination is always genetic
Interesting Facts
the sex of a child is determined at the time of fertilisation
some animals have different methods of sex determination
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2025?
This question carries 4 marks in the CBSE Class 10 Science 2025 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 2025 paper?
This question appears in Section E in the CBSE Class 10 Science 2025 paper.