Consider the following statements regarding the sex chromosomes in humans: 1. Sperms are of two kinds: one containing an X chromosome and the other containing a Y chromosome. 2. An unfertilized egg contains either an X or a Y chromosome. 3. If a sperm with an X chromosome fertilizes the egg, the zygote develops into a female. Which of the statements given above is/are correct?

The correct option is (c) 1 and 3 only. Explanation Human sex determination follows the XX-XY mechanism. Humans have 23 pairs of chromosomes, of which 22 pairs are autosomes and one pair consists of sex chromosomes. Females are homogametic (XX), while males are heterogametic (XY). Statement-wise Analysis: - Statement 1 is Correct: Males possess one X and one Y chromosome (XY). During spermatogenesis (formation of sperms), two types of gametes are produced in equal proportions: 50% of sperms carry the X chromosome, and the other 50% carry the Y chromosome. - Statement 2 is Incorrect: Females possess two X chromosomes (XX). Consequently, all haploid gametes (ova or eggs) produced by a female contain only the X chromosome. An unfertilized egg cannot contain a Y chromosome. - Statement 3 is Correct: The sex of the zygote is determined by the sperm that fertilizes the egg. If a sperm carrying the X chromosome fertilizes the egg (which always carries an X), the resulting zygote will have an XX genotype and develop into a female. Conversely, if a sperm carrying the Y chromosome fertilizes the egg, the zygote will be XY and develop into a male. Key Takeaway: In humans, the sex of the child is determined by the type of sperm (X or Y) that fertilizes the ovum; therefore, the genetic makeup of the father determines the sex of the offspring.

NCERT Class 8 Science — Chapter 4: Reaching the age of adolescence

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Consider the following statements regarding the sex chromosomes in humans:

Sperms are of two kinds: one containing an X chromosome and the other containing a Y chromosome.
An unfertilized egg contains either an X or a Y chromosome.
If a sperm with an X chromosome fertilizes the egg, the zygote develops into a female.

Which of the statements given above is/are correct?

Official previous-year question

Verified 1 Aug 2026.

Options

A1 and 2 only
B2 only
C1 and 3 only
D1, 2 and 3

Did you get this right?

Solution

The correct option is (c) 1 and 3 only.

Explanation

Human sex determination follows the XX-XY mechanism. Humans have 23 pairs of chromosomes, of which 22 pairs are autosomes and one pair consists of sex chromosomes. Females are homogametic (XX), while males are heterogametic (XY).

Statement-wise Analysis:

Statement 1 is Correct: Males possess one X and one Y chromosome (XY). During spermatogenesis (formation of sperms), two types of gametes are produced in equal proportions: 50% of sperms carry the X chromosome, and the other 50% carry the Y chromosome.
Statement 2 is Incorrect: Females possess two X chromosomes (XX). Consequently, all haploid gametes (ova or eggs) produced by a female contain only the X chromosome. An unfertilized egg cannot contain a Y chromosome.
Statement 3 is Correct: The sex of the zygote is determined by the sperm that fertilizes the egg. If a sperm carrying the X chromosome fertilizes the egg (which always carries an X), the resulting zygote will have an XX genotype and develop into a female. Conversely, if a sperm carrying the Y chromosome fertilizes the egg, the zygote will be XY and develop into a male.

Key Takeaway: In humans, the sex of the child is determined by the type of sperm (X or Y) that fertilizes the ovum; therefore, the genetic makeup of the father determines the sex of the offspring.

Your note

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The correct option is (c) 1 and 3 only.

Explanation

Statement-wise Analysis:

Statement 1 is Correct: Males possess one X and one Y chromosome (XY). During spermatogenesis (formation of sperms), two types of gametes are produced in equal proportions: 50% of sperms carry the X chromosome, and the other 50% carry the Y chromosome.
Statement 2 is Incorrect: Females possess two X chromosomes (XX). Consequently, all haploid gametes (ova or eggs) produced by a female contain only the X chromosome. An unfertilized egg cannot contain a Y chromosome.
Statement 3 is Correct: The sex of the zygote is determined by the sperm that fertilizes the egg. If a sperm carrying the X chromosome fertilizes the egg (which always carries an X), the resulting zygote will have an XX genotype and develop into a female. Conversely, if a sperm carrying the Y chromosome fertilizes the egg, the zygote will be XY and develop into a male.