How is Trisomy 13 most often caused?
Trisomy 13 most often occurs randomly as sperm and eggs are created, most commonly due to a process called nondisjunction. Humans generally have 46 chromosomes (23 pairs) in every cell in their body. When a woman’s eggs are made, each egg generally has one copy of each of the 23 chromosomes. The same is true for sperm. The 23 copies from the sperm and the 23 copies from the egg then combine to create an embryo with 46 chromosomes (23 pairs). When nondisjunction happens, an egg or a sperm is created with 2 or 0 copies of a given chromosome instead of the usual 1. If an egg with two copies of chromosome 13 combines with a sperm with 1 copy of chromosome 13, the embryo can develop into a baby who will have trisomy 13.
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