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The aneuploidy is a genomic mutation (numerical chromosomal aberration ), in which individual chromosomes are in addition to the usual set of chromosomes present or absent. If there is no aneuploidy, it is called euploidy .

The following forms can occur:

  • Null isomy : a homologous chromosome pair is missing
  • Monosomy : a single chromosome is missing. Occasionally, the deletion of a larger piece of chromosome is referred to as a "partial monosomy".
  • Polysomy : at least one homologous chromosome is too many, special case trisomy : one homologous chromosome is too many.

Aneuploidies in humans

In contrast to other genetic model organisms, aneuploidy is common in humans. It is estimated that around 10 to 30 percent of fertilized human eggs have an incorrect number of chromosomes (usually trisomy or monosomy). Aneuploidy is therefore a common cause of miscarriages : Around a third of the fetuses screened for miscarriages showed aneuploidy, which makes this the most important single cause . About 0.3 percent of live born children have aneuploidy, mostly either trisomy 21 or aneuploidy of the sex chromosomes .

Because of the different processes involved in meiosis between male and female germ cells (the second meiotic division occurs only after fertilization), errors in the segregation of chromosomes, which lead to aneuploidy, occur more frequently in egg cells than in sperm. So that the physical contact between the chromosomes is not lost during anaphase I, at least one chiasm , caused by crossing-over, is required in each chromosome ; the crossing-over rate is therefore much higher for egg cells than for sperm.

A missing autosome or a lack of the X chromosome in men is lethal - the human being is not viable. Cells with extra gonosomes are viable; extra autosomes usually lead to serious disabilities , if survival is at all possible.

Cancer cells are often aneuploid. The subject of research is whether the aneuploidy of cancer cells is the cause or consequence of the disease.

Aneuploidy screening

Aneuploidy screening is a form of pre-implantation diagnosis (PGD) in which an in vitro generated embryo is examined for the presence of aneuploidy. While PGD is a so-called molecular genetic examination at the DNA level to detect a certain genetic defect, aneuploidy screening is a cytogenetic examination to clarify the number and structure of the individual chromosomes. Aneuploidies are generally considered to be the cause of the majority of fertility disorders . The aim of aneuploidy screening is to select embryos with a normal set of chromosomes ( euploid embryos) for transfer. It is hoped that this will increase the success rate of in vitro fertilization.

Individual evidence

  1. Terry Hassold and Patricia Hunt (2001): To err (meiotically) is human: the genesis of human aneuploidy. Nature Revies Genetics 2: 280-291. doi: 10.1038 / 35066065
  2. Peter Duesberg : The chaos in the chromosomes. In: Spectrum of Science. 10/07, p. 55 ff.
  3. D. Zimonjic, MW Brooks, N. Popescu, RA Weinberg, WC Hahn: Derivation of human tumor cells in vitro without widespread genomic instability. In: Cancer Res. 61 (24), Dec 15, 2001, pp. 8838-8844.
  4. The text of this section originates in whole or in part from the message on the amendment of the constitutional provision on reproductive medicine and genetic engineering in the human sector (Art. 119 BV) as well as the Reproductive Medicine Act (Preimplantation Diagnostics) of June 7, 2013 of the Swiss Federal Council, p. 5862. This text is subject to Art. 5 para. 1 let. c of the Swiss Copyright Act does not affect copyright protection.