A third daughter cell may end up with the missing chromosome. Multipolar spindles: more than two spindle poles form. Such a mitotic division would result in one daughter cell for each spindle pole; each cell may possess an unpredictable complement of chromosomes. Monopolar spindle: only a single spindle pole forms. This produces a single daughter cell with its copy number doubled. A tetraploid intermediate may be produced as the end-result of the monopolar spindle mechanism. In such a case, the cell has double the copy number of a normal cell, and produces double the number of spindle poles as well. This results in four daughter cells with an unpredictable complement of chromosomes, but in the normal copy number. Somatic mosaicism in the nervous system
Mosaicism for aneuploid chromosome content may be part of the constitutional make-up of the mammalian brain. In the normal human brain, brain samples from six individuals ranging from 2–86 years of age had mosaicism for chromosome 21 aneuploidy (average of 4% of neurons analyzed). This low-level aneuploidy appears to arise from chromosomal segregation defects during cell division in neuronal precursor cells, and neurons containing such aneuploid chromosome content reportedly integrate into normal circuits. However, recent research using single-cell sequencing has challenged these findings, and has suggested that aneuploidy in the brain is actually very rare. Somatic mosaicism in cancer
Aneuploidy is consistently observed in virtually all cancers. The German biologist Theodor Boveri was first to propose a causative role for aneuploidy in cancer.
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.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. DNA methylation and histone modifications comprise two of the main epigenetic modifications important for many physiological and pathological conditions, including cancer. Aberrant DNA methylation is the most common molecular lesion in cancer-cells, even more frequent than gene mutations. 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. Some of the alterations have been correlated with the formation of aneuploid cells in vivo. In this study it is suggested on a growing basis of evidence, that not only genetics but also epigenetics, contribute to aneuploid cell formation. Partial aneuploidy
The terms "partial monosomy" and "partial trisomy" are used to describe an imbalance of genetic material caused by loss or gain of part of a chromosome. In particular, these terms would be used in the situation of an unbalanced translocation, where an individual carries a derivative chromosome formed through the breakage and fusion of two different chromosomes.