Question

What causes Down Syndrome?

Nondisjunction during mitosis resulting in Monosomy 21
Disjunction during mitosis causing one less copy of chromosome 18 in each cell
When an individual has 46 chromosomes in each cell
Nondisjunction during meiosis resulting in Trisomy 21

Answer 1

Down syndrome is caused by having three copies of chromosome 21, which is known as trisomy 21. The most common cause of trisomy 21 is chromosomal nondisjunction during meiosis. The frequency of nondisjunction events increases with maternal age.

Step-by-step explanation:

Down syndrome is caused by having three copies of chromosome 21, which is known as trisomy 21. The most common cause of trisomy 21 is chromosomal nondisjunction during meiosis. Nondisjunction occurs when the chromosomes do not divide equally among gametes, resulting in an extra chromosome 21. This can happen during meiosis in the egg or sperm cell. The frequency of nondisjunction events increases with maternal age, which is why the risk of having a child with Down syndrome increases in older women.