Disjunction is the separation of chromosomes during anaphase I and II in meiosis. After fertilization the four resultant zygotes have both members of each homologous pair (in this case, of the one homologous pair called in the diploid cell) and are said to be disomic(normal).
Sometimes the chromatids of a tetrad or dyad(double) fail to separate in meiosis I or II. This event is called non-disjunction. The products of non-disjunction are aneuploid, a condition in which the chromosome number is not an exact multiple of the haploid (1n) cell. In this tutorial you will examine chromosome disjunction errors that can occur during meiosis and how the gamete genomes are affected by these errors.
