The most frequently occurring form of Down syndrome results from
A) an extra broken piece of a twenty-first chromosome attaching to another chromosome.
B) an error during the early stages of mitosis.
C) a failure of the twenty-first pair of chromosomes to separate during meiosis.
D) the inheritance of an extra X chromosome.

Question

Quizplus · Accepted Answer

The most common form of Down syndrome, known as Trisomy 21, occurs when the twenty-first pair of chromosomes fail to separate during meiosis, resulting in an individual with three copies (trisomy) of chromosome 21 instead of the usual two copies. This accounts for approximately 95% of cases of Down syndrome.

The Most Frequently Occurring Form of Down Syndrome Results from