Question

The diagram represents the chromosomes of a person with a genetic disorder caused by non disjunction in which the chromosomes fail to separate properly. Which chromosome set display non-disjunction? What is the syndrome?

• A. Chromosome set 21; Down's syndrome
• B. Chromosome set 21; Klinefelter's syndrome
• C. Chromosome set 23; Klinefelter's syndrome
• D. Chromosome set 23; Turner's syndrome

Answer 1

Answer: (A)

Chromosome set 21; Down's syndrome

In the diagram given above, we can clearly see three copies of chromosome 21. Disorder related to this is known as Down syndrome, that causes developmental and intellectual delays.

Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21. Common physical traits are low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the centre of the palm. Each individual with Down syndrome is a unique individual and may possess these characteristics to different degrees.

Down syndrome is usually caused by an error in cell division called non-disjunction. It results in an embryo with three copies of chromosome 21 instead of the usual two.