Question

question 11

what happens, chromosomally, to cause down syndrome?

there is one less chromosome in pair 21.
there is an extra chromosome in pair 21.
there is a partial deletion of one chromosomes in pair 21.
both chromosomes are missing in pair 21.

Explanation:

Identify the chromosomal basis of Down syndrome

Using the Chromosomal Abnormalities knowledge point

• Down syndrome is also known as Trisomy 21.
• It is caused by the presence of a third copy of chromosome 21.
• This means there is an extra chromosome in pair 21.

Answer:

• There is one less chromosome in pair 21.
• There is an extra chromosome in pair 21. (Correct answer)
• There is a partial deletion of one chromosomes in pair 21.
• Both chromosomes are missing in pair 21.