Down syndrome, a genetic disorder, is caused by an abnormality in the:

Correct answer: Chromosome. Down syndrome results from an extra copy of chromosome 21, so it is a chromosomal abnormality.

Background: Chromosomes carry genes, which are made of DNA.

• DNA: DNA is the genetic material but the abnormality here is in the number of chromosomes.
• Plasma: Plasma is the liquid part of blood.
• None of these: “None of these” is incorrect because chromosome is correct.

Did you know? A normal human cell has 46 chromosomes.

Memory trick: Down = extra chromosome 21.