Chapter 11, Problem 26A

Summary Introduction

Introduction:

The study of genetics does not involve study of genes alone. Scientists also study chromosomes by using images of chromosomes stained during metaphase. Chromosomes are the structures that contain the genetic material that are passed from generation to generation of cells. The pairs of homologous chromosomes are arranged in order of decreasing size to produce a micrograph called karyotype.

Answer to Problem 26A

Correct answer :

The correct answer is option C. Down syndrome

Explanation of Solution

Explanation/justification for the correct answer:

Option C. Down syndrome − The given karyotype shows an extra copy of chromosome 21. This causes a chromosomal disorder called Down syndrome. It is also called trisomy 21. The symptoms of this disorder are short stature, heart defects and mental disabilities.

Hence this option is the correct option.

Explanation for incorrect answer:

Option A. Turner’s syndrome − This occurs when one X chromosome is missing in females. So the karyotype for this syndrome will show a missing X chromosome. The given karyotype shows an extra copy of chromosome 21. This causes a chromosomal disorder called Down syndrome. Hence, this is not the correct option.

Option B. Klinefelter’s syndrome- This occurs when one extra X chromosome is present in males. So the karyotype for this syndrome will show an extra X chromosome in sex chromosomes. The given karyotype shows an extra copy of chromosome 21. This causes a chromosomal disorder called Down syndrome. Hence, this is not the correct option.

Option D. The karyotype shows no disorder- The karyotype shows a disorder called Down syndrome due to an extra copy of chromosome 21. Hence this is not the correct option.