What is nondisjunction?

Nondisjunction refers specifically to the failure of homologous chromosomes or sister chromatids to separate properly during cell division, particularly during meiosis. This results in gametes that contain an abnormal number of chromosomes. If such a gamete is involved in fertilization, it can lead to conditions such as Down syndrome, which is caused by an extra copy of chromosome 21.

Understanding nondisjunction is crucial in genetics because it has direct implications for the genetic diversity and viability of offspring. It can lead to aneuploidy, which is a condition where a cell has an abnormal number of chromosomes, hence affecting the developmental processes and overall health of the organism.

The process of gamete formation involves the separation of alleles, but that is a different concept regarding Mendelian inheritance rather than nondisjunction. Furthermore, the creation of genetically identical cells relates to mitosis rather than meiosis and nondisjunction, while combining genetic material from two parents describes sexual reproduction rather than an error in chromosome segregation.