Human Genetics Problem Set

Problem 7: Down's Syndrome

A.	The frequency increases dramatically in mothers over the age of 40.
B.	The cause is a nondisjunction when chromosomes do not separate during the first meiotic division.
C.	Affected individuals have an extra autosome.
D.	The long time lag between onset of meiosis in ovarian tissue (during fetal development) and its completion (at ovulation) is most likely the reason for increased incidence in older mothers.
E.	None, all statements are true. Down's syndrome is also known as trisomy 21.