Question

sara has an extra chromosome on her 21st pair of chromosomes. which disorder does sara have?
○ hemophilia
○ fragile x syndrome
○ sickle-cell anemia
● down syndrome

Explanation:

Hemophilia is a blood - clotting disorder related to X - linked inheritance. Fragile X syndrome is associated with a mutation on the X chromosome. Sickle - cell anemia is a blood disorder caused by a mutation in the gene for hemoglobin. Down syndrome is caused by having an extra chromosome (trisomy) on the 21st pair of chromosomes. Since Sara has an extra chromosome on her 21st pair, she has Down syndrome.

Answer:

Down syndrome