Health Dictionary
Reliable, easy-to-read patient information on common medical conditions — written in plain language, free of jargon, and grounded in current evidence. Browse the most frequent diagnoses, understand what they mean for everyday life, and learn which steps and questions help you have a focused conversation with your doctor.
Maternal age effect
Introduction
The maternal age effect describes the exponentially increasing risks for numerical chromosomal abnormalities among her gametes as a prospective mother ages. This increase reflects the overall increase in the rate of nondisjunction with maternal age.
However, 50% of Down Syndrome cases are actually due to paternal age effect, as are most non-familial genetic disorders. This is because a woman’s ova only divide a total of 24 times throughout life, the first 23 of which happen in utero, whereas men’s sperm divide continuously throughout life, leading to gradually increasing copy errors. Trisomy 21 derived from maternal age effect is due to an error when the egg splits.
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