Nondisjunction
DNA replication duplicates every strand of DNA so that there
are two copies of every chromosome. These (attached) copies, called sister chromatids,
undergo two rounds of chromosomal divisions ( Meiosis I and II). A total of
four haploid cells are now present. Homologous chromosomes or sister chromatids
are pulled apart in a process called disjunction. However, chromosomes may at
times fail to separate properly. This is called nondisjunction.
