Question

What type of chromosomal abnormality leads to the phenotype known as down syndrome?

Answer 1

Trisomy 21.

Step-by-step explanation:

Down syndrome (DNS, DS) is a genetic disorder which is also called as trisomy 21. It is caused by the presence of third copy of chromosome 21.

Trisomy 21: In this syndrome an extra chromosome or chromosome 21 originates in the development of either the egg or the sperm. When the egg and the sperm fertilized to form an egg, three chromosome 21 are present rather than two. As the cell division occur the extra chromosome is repeated in every cell.

Some symptoms of down syndromes are:

1) Delayed physical growth.

2) Mild to moderate intellectual disability.

3) Characteristics facial features.