___ occurs when there is an extra chromosome in the 21?? pair of chromosomes.
A) Down syndrome
B) Sickle-cell anemia
C) Listeria
D) PKU

Question

Quizplus · Accepted Answer

Down syndrome is caused by an extra copy of chromosome 21, resulting in a total of 47 chromosomes instead of the typical 46. Sickle-cell anemia is caused by a genetic mutation affecting hemoglobin, Listeria is a type of bacteria, and PKU is a genetic disorder affecting the body's ability to process phenylalanine. None of these are related to an extra chromosome in the 21st pair.

___ Occurs When There Is an Extra Chromosome in the 21