In 95% of cases of Down's syndrome,there is one extra chromosome (number 21)in every cell.This aneuploid condition is most likely the result of

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Down's syndrome is caused by an extra copy of chromosome 21. This suggests that nondisjunction occurred during meiosis, specifically in meiosis I, where homologous pairs of chromosomes fail to properly separate. This results in one cell having an extra copy of chromosome 21 and the other cell lacking chromosome 21. When these cells are fertilized, the resulting zygote will have three copies of chromosome 21, resulting in Down's syndrome.

In 95% of Cases of Down's Syndrome,there Is One Extra