Aneuploidiesabnormalities

Aneuploidiesabnormalities, often shortened to aneuploidies, refer to conditions where an organism possesses an abnormal number of chromosomes. This deviation from the typical diploid set (two copies of each chromosome) can involve the gain or loss of one or more chromosomes. Aneuploidy is a significant cause of spontaneous abortions and is associated with various developmental disorders in live births.

The most common cause of aneuploidy is nondisjunction, a failure of chromosomes or chromatids to separate correctly during cell division, either meiosis (which produces gametes) or mitosis (which produces somatic cells). If nondisjunction occurs during meiosis, it can lead to gametes with an extra chromosome (trisomy) or a missing chromosome (monosomy). When such a gamete fuses with a normal gamete during fertilization, the resulting zygote will have an abnormal chromosome number. For example, Down syndrome is caused by trisomy 21, meaning individuals have three copies of chromosome 21 instead of the usual two. Turner syndrome, characterized by monosomy X, results from the absence of one sex chromosome in females.

Aneuploidy can also arise from mitotic nondisjunction during embryonic development, leading to mosaicism, where an individual has cells with different chromosome numbers. While some forms of aneuploidy are incompatible with life, others can result in individuals with varying degrees of intellectual disability and physical characteristics. Genetic testing, such as karyotyping or chromosomal microarray analysis, is used to diagnose aneuploidies.