Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more complete sets of chromosomes. A cell with any number of complete chromosome sets is called a euploid cell.An extra or missing chromosome is a common cause of some genetic disorders. Some cancer cells also have abnormal numbers of chromosomes. About 68% of human solid tumors are aneuploid. Aneuploidy originates during cell division when the chromosomes do not separate properly between the two cells (nondisjunction). Most cases of aneuploidy in the autosomes result in miscarriage, and the most common extra autosomal chromosomes among live births are 21, 18 and 13. Chromosome abnormalities are detected in 1 of 160 live human births. Autosomal aneuploidy is more dangerous than sex chromosome aneuploidy, as autosomal aneuploidy is almost always lethal to embryos that cease developing because of it. Chromosomes
Most cells in the human body have 23 pairs of chromosomes, or a total of 46 chromosomes. (The sperm and egg, or gametes, each have 23 unpaired chromosomes, and red blood cells at first in bone marrow have nucleus but those red blood cells that are active in blood lose their nucleus and thus they have no nucleus and no chromosomes. )One copy of each pair is inherited from the mother and the other copy is inherited from the father.
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.