What is the leading cause of Down syndrome?
A) Aberrant implantation in the uterus leads to developmental problems in the fetus.
B) In older females, chromosome 21 is duplicated leading to abnormal egg formation.
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 men over 25, sperm formation is impaired and produces monosomic children.
Answer: C
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