Final answer:
Mitotic nondisjunction describes the improper separation of chromosomes in a somatic cell, leading to cells with abnormal chromosome numbers. This differs from meiosis, where nondisjunction can occur in two stages, potentially resulting in gametes with missing or duplicated chromosomes, affecting genetic variation and potentially leading to disorders like Down syndrome.
Step-by-step explanation:
Improper separation of chromosomes can occur after fertilization in one of the body's somatic cells due to a process known as mitotic nondisjunction. This event can lead to various chromosome disorders. Typically, nondisjunction is associated with errors during meiosis, either in meiosis I or meiosis II. In meiosis I, if homologous chromosomes fail to separate, it results in gametes with missing or duplicated chromosomes. Similarly, nondisjunction during meiosis II occurs when sister chromatids fail to separate properly. This could lead to the production of gametes with an abnormal number of chromosomes, albeit to a different extent than errors in meiosis I.
Unlike meiosis, which occurs in sex cells (gametes), mitotic nondisjunction happens in somatic cells and can result in cells with an extra or missing chromosome. This can have significant consequences for the organism, including genetic disorders like Down syndrome. The cellular division known as mitosis should normally produce two daughter cells that are genetically identical to each other and to the parent cell, with each cell inheriting an exact copy of chromosomes from the parent cell. When nondisjunction occurs during mitosis, this process is disrupted, leading to cells with an aberrant number of chromosomes.