Type of Mutation

4% of the time the extra chromosome comes from the fathers sperm

90% of the time the extra copy comes from the mothers egg

That Causes Down Syndrome

Down Syndrome is an extra complete or incomplete chromosome

This can be caused by Non-Disjunction which is when the sister chromosomes fail to separate properly in cell division

No behavioral activity of the parents or environmental factors are known to cause Down Syndrome

In other cases the chromosome is copied when the embryo is growing