Nondiszjunkció

Nondiszjunkció, also known as chromosome mis-segregation, is an error in cell division that occurs during meiosis or mitosis. During normal cell division, homologous chromosomes or sister chromatids separate and move to opposite poles of the cell. Nondiszjunkció happens when these chromosomes or chromatids fail to separate properly.

In meiosis, nondiszjunkció can lead to the formation of gametes (sperm or egg cells) with an abnormal number of chromosomes. This can result in aneuploidy, a condition where a cell has an extra chromosome or is missing a chromosome. For example, in humans, nondiszjunkció during meiosis can cause conditions like Down syndrome (trisomy 21), where an individual has three copies of chromosome 21 instead of the usual two. Other examples include Edwards syndrome (trisomy 18) and Patau syndrome (trisomy 13).

Nondiszjunkció can also occur during mitosis, the process of somatic cell division. While less commonly discussed in the context of inherited disorders, mitotic nondiszjunkció can lead to mosaicism, where an individual has cell populations with different chromosome numbers. This can have implications for development and health, depending on the tissues affected and the timing of the error.

The exact causes of nondiszjunkció are not fully understood, but factors such as advanced maternal age, exposure to certain environmental agents, and errors in the spindle apparatus that guides chromosome movement are suspected contributors. Understanding nondiszjunkció is crucial for diagnosing and counseling individuals with chromosomal abnormalities.