Down syndrome, the most common genetic condition in the united states, is also called trisomy 21. what does this mean?

Explanation:

It means that chromosome 21 has a third partial or complete copy of chromosome 21. The symptom severities vary somewhat.

There are three set of chromosome 21

Explanation:

Trisomy signifies presence of abnormal three chromosomes instead of two.

Down syndrome is also known as trisomy 21 because there are three chromomose -21 rather than two.

There are 46 chromosome in a normal human being which constitutes 23 pairs of chromosome. However, a person suffering from down syndrome has 47 chromosome with an extra chromosome -21.

the answer is b: 1.4 km/hr