Question 181 markMCQSection A

Assertion (A) : Human female has a perfect pair of sex chromosome.

Reason (R) : Sex chromosome contributed by the human male in the zygote decides the sex of a child.

Heredity
Sex Determination

Options

(A)Both (A) and (R) are true and (R) is the correct explanation of (A).
(B)Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(C)(A) is true, but (R) is false.
(D)(A) is false, but (R) is true.

Official answer

The correct option is B.

Answer keywords:perfect pairsex chromosomesXXXYfather determines sexindependent statements

Marking scheme

  1. 1.1 mark for selecting the correct option B.

Hint

Determine if both statements are individually true. Then check if the mechanism of sex determination by the father's sperm explains why females have two identical XX chromosomes.

Quick oral answer

In humans, females have two identical sex chromosomes (XXXX), making it a perfect pair. Males have a mismatched pair (XYXY). Since females only produce gametes with XX chromosomes, the sex of the child is determined solely by whether the fertilizing sperm carries an XX or a YY chromosome from the father.

Common mistakes

  1. 1.Students often choose option A thinking that because both statements are about sex chromosomes and sex determination, one must explain the other.
  2. 2.Some students mistakenly believe that females have mismatched chromosomes.

Analysis and explanation

The Assertion (A) states that a human female has a perfect pair of sex chromosomes. According to the NCERT text, 'Women have a perfect pair of sex chromosomes, both called X.' Thus, Assertion (A) is true. The Reason (R) states that the sex chromosome contributed by the human male in the zygote decides the sex of a child. According to the NCERT text, 'the sex of the children will be determined by what they inherit from their father. A child who inherits an X chromosome from her father will be a girl, and one who inherits a Y chromosome from him will be a boy.' Thus, Reason (R) is also true. However, the fact that the father's sex chromosome determines the sex of the child does not explain why females have a perfect pair of sex chromosomes (XXXX). The two statements are independent biological facts. Therefore, both (A) and (R) are true, but (R) is not the correct explanation of (A).

Interesting facts

In some reptiles, sex is determined by environmental temperature during egg incubation, whereas in humans, it is strictly genetically determined by the sex chromosome carried by the sperm.

Question details

Q18 of 39 questions

Board
CBSE
Class
Class 10
Subject
Science
Year
2024
Section
Section A
Marks
1
Type
MCQ
Chapter
Heredity
Topic
Sex Determination
Bloom's level
Analyzing
Syllabus topic
Sex determination: Brief introduction

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Frequently asked questions

How many marks does this question carry in CBSE Class 10 Science 2024?

This question carries 1 mark in the CBSE Class 10 Science 2024 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 2024 paper?

This is a MCQ question from Section A in the CBSE Class 10 Science 2024 paper.