What causes chromosomal aberrations?

Chromosomal abnormalities typically arise from mistakes during cell division, primarily mitosis or meiosis. Errors during meiosis, particularly nondisjunction, where chromosomes fail to separate properly, can lead to aneuploidy. This results in sex cells with an extra or missing chromosome. If fertilization occurs with such affected cells, the resulting offspring may have chromosomal disorders. Structural chromosomal abnormalities, which are less common, involve duplicated, inverted, missing, or fused chromosome segments. When these occur after meiosis, they can result in offspring inheriting either two or no copies of a chromosome, leading to conditions like monosomy or trisomy. Mosaicism involves individuals having multiple cell lines with different chromosomal compositions. This can arise from mitotic nondisjunction during early embryonic development, resulting in some cell lines with abnormalities while others remain unaffected.