Question

In which parent does nondisjunction most commonly occur to cause Down's Syndrome?

Options

• Mother (during oogenesis)

• Mitotic error in the embryo

• Father (during spermatogenesis)

• Both parents equally

Answer 1

Maternal nondisjunction during oogenesis accounts for approximately 95% of Down's Syndrome cases. The risk of nondisjunction increases significantly with advanced maternal age, with the risk substantially higher in women over 35 years old. This age-related effect is primarily responsible for the increased incidence of Down's Syndrome in births to older mothers.