What is the Leading Cause of Down Syndrome

Question

What is the leading cause of Down syndrome?
A)In men over 25,sperm formation is impaired and produces monosomic children.
B)Aberrant implantation in the uterus leads to developmental problems in the fetus.
C)The nondisjunctional event that produces Down syndrome occurs more frequently during oogenesis in women older than age 35.
D)In older parents,there is egg/sperm incompatibility leading to duplication of chromosome 21.
E)In older females,chromosome 21 is duplicated leading to abnormal egg formation.

Accepted Answer

The nondisjunctional event that produces Down syndrome occurs more frequently during oogenesis in women older than age 35. This means that an error in cell division during the development of the egg cell results in an extra copy of chromosome 21, which is then passed on to the offspring. This is the most common cause of Down syndrome, accounting for about 95% of cases.