As women age, oocytes develop defects in mitochondrial structure and function and have meiotic spindle dysregulation: these increase rates of aneuploidy and miscarriage.

During meiosis, when germ cells divide to create sperm and egg (gametes), each half should have the same number of chromosomes.

In general, individuals who are mosaic for a chromosomal aneuploidy tend to have a less severe form of the syndrome compared to those with full trisomy.

[citation needed] Aneuploidy arises from errors in chromosome segregation, which can go wrong in several ways.

[citation needed] Mosaicism for aneuploid chromosome content may be part of the constitutional make-up of the mammalian brain.

[16] However, recent research using single-cell sequencing has challenged these findings, and has suggested that aneuploidy in the brain is actually very rare.

[20] Understanding through what mechanisms it can affect tumor evolution is an important topic of current cancer research.

[24] Loss of tumor suppressor p53 gene often results in genomic instability, which could lead to the aneuploidy genotype.

This has therefore suggested that the presence of an abnormal number of chromosomes might be an effective predictive biomarker for response to precise immunotherapy.

For example, in melanoma patients, high somatic copy number alterations are associated with less effective response to immune checkpoint blockade anti–CTLA4 (cytotoxic T lymphocyte–associated protein 4) therapy.

[21] A research work published in 2008 focuses on the mechanisms involved in aneuploidy formation, specifically on the epigenetic origin of aneuploid cells.

Epigenetic inheritance is defined as cellular information other than the DNA sequence itself, that is still heritable during cell division.

Tumor suppressor gene silencing by CpG island promoter hypermethylation is supposed to be the most frequent epigenetic modification in cancer cells.

Epigenetic characteristics of cells may be modified by several factors including environmental exposure, deficiencies of certain nutrients, radiation, etc.

In this study it is suggested on a growing basis of evidence, that not only genetics but also epigenetics, contribute to aneuploid cell formation.

Exposure of males to lifestyle, environmental and/or occupational hazards may increase the risk of spermatozoa aneuploidy.

Occupational exposure of pesticide factory workers to fenvalerate is associated with increased spermatozoa DNA damage.

[37] Men contaminated with PFCs in whole blood or seminal plasma have spermatozoa with increased levels of DNA fragmentation and chromosomal aneuploidies.

[citation needed] These tests can also be performed prenatally to detect aneuploidy in a pregnancy, through either amniocentesis or chorionic villus sampling.

Recent advances have allowed for less invasive testing methods based on the presence of fetal genetic material in maternal blood.