Nondisjuction Before and After Conception

Two nondisjunctions happen here

Only the chromosomes 21 have been shown in this diagram.
However, the cells contain either 46 or 47 chromosomes (with two 21's, shown as open circles)
or 47 chromosomes (three 21's, shown as filled circles).

©1996 Dept. of Human Genetics, Medical College of Virginia / Virginia Commonwealth Univ.
Used with permission of authors

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