nondiszjunkiója

Nondiszjunkiója, often translated as "nondisjunction," refers to the failure of homologous chromosomes or sister chromatids to separate properly during cell division. This error can occur during meiosis, the process that produces gametes (sperm and egg cells), or during mitosis, the process of somatic cell division.

When nondisjunction happens during meiosis, it leads to gametes with an abnormal number of chromosomes. If homologous chromosomes fail to separate in meiosis I, each daughter cell receives an incorrect number of chromosomes. If sister chromatids fail to separate in meiosis II, then two of the four resulting gametes will have an abnormal number of chromosomes, while the other two will be normal. If nondisjunction occurs during mitosis, it can result in a condition called mosaicism, where an individual has populations of cells with different chromosome numbers.

The consequences of nondisjunction depend on when and where it occurs. In humans, nondisjunction during meiosis is a significant cause of chromosomal abnormalities in offspring. For example, nondisjunction of chromosome 21 leads to Down syndrome, characterized by specific physical and intellectual developmental features. Nondisjunction can also result in other aneuploidies, such as Turner syndrome (monosomy X) and Klinefelter syndrome (XXY). The likelihood of nondisjunction, particularly in human eggs, increases with maternal age.