The failure of chromosome pairs to separate properly during cell division.
The most common deffect that will occur with there is nondisjunction on the 21st chromosome is downs syndrome. Downs syndrome is a mental illness that can cause some physical abnormalities such as a large forhead, but also some intellectual delays.
nondisjunction |ˌnändisˈjə ng k sh ən| noun Genetics the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.
Down syndrome happens by the splitting of the chromosomes. It is not a genetic disease. It is a chromosomaldisorder.Chromosomal changes like duplications or translocations1 occur in only one sex cell. A baby normally inherits 23 chromosomes from each parent to make a total of 46 chromosomes in 23 identifiable pairs.In Down Syndrome, an extra (duplicated) chromosome number 21 is inherited from either the father or the mother, to make a total of 47 chromosomes (23 pairs plus 1) in every cell of the DS child. (DS is also called Trisomy 21 ) DS is usually inherited from the mother, and the major risk of DS is the age of the woman at conception.1A duplication is an extra copy of a chromosome (or part of a chromosome) - a translocation is an extra bit of chromosome sticking onto another chromosome.