Answer the following question given this paragraph: 

One common example of an extra-chromosome disorder is Down syndrome ( Figure below ). Children with Down syndrome are mentally disabled and also have physical deformities. Down syndrome occurs when a baby receives an extra chromosome 21 from one of his or her parents. Usually, a child will receive one chromosome 21 from the mother and one chromosome 21 from the father. In an individual with Down syndrome, however, there are three copies of chromosome 21 ( Figure below ). Therefore, Down syndrome is also known as Trisomy 21. These people have 47 total chromosomes.


Q: What's the most common disorder from having an extra chromosome?

 Choices:

- Williams syndrome

- Turner syndrome

- cri-du-chat syndrome

- down syndrome

A:
down syndrome
