Chapter 14, Problem 7STP

Summary Introduction

Introduction:

Human females have 22 pairs of autosomes and one pair of X chromosomes. Females have two doses of X chromosomes while males have only one dose. To balance the difference in the dose of X- related genes, one of the X chromosomes stops working or becomes inactivated. This is called dosage compensation and is a random event.

Answer to Problem 7STP

Correct answer :

The correct answer is option B. female sex cells

Explanation of Solution

Explanation/justification for the correct answer:

Option B. female sex cells − The inactivated X chromosomes can be observed in cells. In 1949 Murray Barr observed inactivated X chromosomes in female calico cats. He noticed a darkly stained structure in the nucleus. These structures are called Barr bodies and are found in only female X chromosomes. Hence this is the correct option.

Explanation for incorrect answer:

Option A. female body cells − The darkly stained structures in nuclei of cells are called Barr bodies and are found in only female sex chromosomes. Barr bodies are inactivated X chromosomes. They are not found in female body cells. Hence this is not the correct option.

Option C. male body cells - The darkly stained structures in nuclei of cells are called Barr bodies and are found in only female sex chromosomes. Barr bodies are inactivated X chromosomes. They are not found in male body cells. Hence this is not the correct option.

Option D. male sex cells − The darkly stained structures in nuclei of cells are called Barr bodies and are found in only female sex chromosomes. Barr bodies are inactivated X chromosomes. They are not found in male sex cells. Hence this is not the correct option.