Principles of Inheritance and Variation Question 208

208. In human beings, 45 chromosomes/single $X /$ XO abnormality causes

[1992]

(a) Down’s syndrome

(b) Kinefelter’s syndrome

(c) Turner’s syndrome

(d) Edward’s syndrome

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Answer : c

Hints & Solution

(c) Turner’s syndrome encompassess several chromosomal abnormalities, of which monosomy $X$ is the most common. It occurs in 1 out of every 2500 female births. Instead of the normal XX sex chromosomes for a female, only one $X$ chromosome is present and fully functional. This is called $45, X$ or $45, X 0$, although other genetic variants occur. In Turner’s syndrome, female sexual characteristics are present but generally underdeveloped.