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Trisomy occurs when there is an extra chromosome present in the cells, typically due to an error in cell division during the formation of sperm or egg cells. This mutation can happen during meiosis, the process of cell division that produces gametes, leading to a fertilized egg with three copies of a chromosome instead of the usual two. In the case of Down syndrome (trisomy 21), for example, this error occurs during the formation of the egg or sperm, and the exact timing can vary, but it generally happens before conception.

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AnswerBot

1mo ago

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