Explain with the help of a flow chart that in human beings father is responsible for the sex (male or female) of the child.

Heredity

Sex Determination

Official Answer

In human beings, the sex of an individual is genetically determined by the sex chromosomes inherited from the parents.

Chromosomal Makeup:

Females have a perfect pair of sex chromosomes, represented as $XX$ . All female gametes (eggs) carry only the $X$ chromosome.
Males have a mismatched pair of sex chromosomes, represented as $XY$ . Male gametes (sperms) are of two types: half carry the $X$ chromosome and the other half carry the $Y$ chromosome.

Role of the Father:

Since the mother always contributes an $X$ chromosome to the child, the sex of the child depends entirely on the type of sex chromosome contributed by the father's sperm.
If a sperm carrying the $X$ chromosome fertilizes the egg, the zygote will be $XX$ (female child).
If a sperm carrying the $Y$ chromosome fertilizes the egg, the zygote will be $XY$ (male child).

Thus, the father is solely responsible for determining the sex of the child.

Father (XY)Mother (XX)SpermEggX chromosomeY chromosomeFertilizationSex determination

Marking Scheme

11 mark
21 mark

Hint

Remember that the mother always contributes an $X$ chromosome. Focus on what the father can contribute ( $X$ or $Y$ ) and how that decides the final combination ( $XX$ or $XY$ ).

Quick Oral Answer

In humans, females have two $X$ chromosomes ( $XX$ ) and males have one $X$ and one $Y$ chromosome ( $XY$ ). Since the mother always gives an $X$ chromosome, the sex of the child depends entirely on whether the father's sperm carries an $X$ chromosome (resulting in a girl) or a $Y$ chromosome (resulting in a boy).

Analysis & Explanation

The genetic mechanism of sex determination in humans is XY-type. The mother is homogametic ( $XX$ ) and can only pass on an $X$ chromosome. The father is heterogametic ( $XY$ ) and can pass on either an $X$ or a $Y$ chromosome. Therefore, the sperm from the father determines the genetic sex of the zygote at the moment of fertilization.

Common Mistakes

1Many students draw a complex Punnett square but forget to explicitly state the conclusion that the father's sperm is the deciding factor. Some mistakenly write that mothers can also contribute a Y chromosome.

Interesting Facts

In many societies, women are falsely blamed for giving birth to female children, but biologically, it is the father's genetic contribution (sperm) that determines the sex of the child.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2025?

This question carries 2 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 is a Very Short Answer question from Section B in the CBSE Class 10 Science 2025 paper.