A chromosomal abnormality that results from an extra portion of the 21st chromosome is known as:
A) phenylketonuria.
B) Down Syndrome.
C) Fragile X syndrome.
D) hemophilia.

Question

Quizplus · Accepted Answer

Down Syndrome is caused by an extra copy (either full or partial) of chromosome 21, leading to a total of three copies instead of the usual two, which is why it's also known as trisomy 21.

A Chromosomal Abnormality That Results from an Extra Portion of the 21st