Question

Down syndrome is caused by nondisjunction of chromosome pair 21. If a person with Down syndrome has a child with a person who does not have Down syndrome, what is the probability that the child will have Down syndrome?

0%

50%

75%

100%

Answer 1

If you want to show off you can say that none of the answers is quite right, although 0% is the closest option. A rare form of familial Down's can come from a translocation of part of chromosome 21 onto another chromosome. This accounts for 2-3% of Down's syndrome cases. Normally the condition is not passed on.