(C) The symptoms described,such as short neck,stubby hands,slanting eyes,permanently open mouth,and short stature,are characteristic of Down syndrome.

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An extra chromosome in the $21^{st}$ pair of autosomes

(C) The symptoms described,such as short neck,stubby hands,slanting eyes,permanently open mouth,and short stature,are characteristic of Down syndrome.Down syndrome is a chromosomal disorder caused by the presence of an additional copy of chromosome number $21$ (trisomy of $21$).This results in a total of $47$ chromosomes in the affected individual instead of the normal $46$.

Class 12 Biology Principles of Inheritance and Variation Chromosomal disorders

Medium

An abnormal male child is born to normal parents. This child shows a short neck,stubby hands,slanting eyes,a permanently open mouth with a projecting upper lip,and short stature. This abnormality can be attributed to:

A
An extra $Y$ chromosome
B
An extra $X$ chromosome
C
An extra chromosome in the $21^{st}$ pair of autosomes
D
Absence of $X$ chromosome leading to a total of $45$ chromosomes instead of the normal $46$