E. None, all statements are true. Down syndrome is also known as Trisomy 21. Information about Down Syndrome. An extra copy of chromosome 21 Individuals with Down syndrome have either an extra copy of chromosome 21, or a segment of chromosome 21 translocated to another chromosome. The three copies of the genetic information from segments of chromosome 21 results in Down syndrome.
Meiotic errors lead to chromosome aneuploidy .
A pair of homologous chromosomes may fail to separate during the first Meiotic division. This phenomenon is called nondisjunction. If the paired chromosomes fail to separate during meiosis in the female, then the resulting daughter cells will receive either 2 or no copies of chromosome 21. If the resulting egg with 2 copies of chromosome 21 is fertilized with a normal sperm, the resulting zyote with be Trisomy 21. Effect of mother's age Mothers in their 40's are much more likely to have a child with Down syndrome than younger mothers.