Easy and brief description of non-disjunction

Non-disjunction

Definition: Non- disjunction occurs in cell division when chromosomes do not divide properly.

 Normally, when a cell divides, the chromosomes line up in an orderly way and then separate from each other before cell division.

When these chromosomes fail to separate properly, non-disjunction has occurred

 The resulting daughter cells have an incorrect number of chromosomes;

one may have too many, while another may have too few.

This causes problems in cell function because a cell cannot function normally without the right amount of chromosomes.

In  Mitosis

Each chromosome is composed of two identical sister chromatids. During the anaphase stage, these chromatids normally separate, and one chromatid goes into each daughter cell. However, when nondisjunction occurs, the chromatids do not separate. The result is that one cell receives both chromatids, while the other cell receives neither.  when mitosis is complete; one cell has an extra chromosome, while the other is missing one.

In Meiosis I, a pair of homologous chromosomes does not separate due to non-disjunction.

So the resulting cells, one cell has two copies of a chromosome, while the other cell has no copies. The four total cells produced will all have chromosomal abnormalities.

In  Meiosis II, like mitosis;  a pair of sister chromatids fail to separate properly so  one daughter cell will have an extra chromosome and one daughter cell will be missing a chromosome.