Causes of chromosomal aberration
There are different causes for the numerical and structural chromosomal aberrations. The numerical chromosomal aberration has a different number of chromosomes, but the chromosomes themselves look normal. In aneuploidy, single chromosomes are duplicated or missing, as in trisomy 21, for example, the most common cause is non-disjunction of chromosomes during meiosis.
Meiosis has the function of producing germ cells. These contain a one-chromatide chromosome as the genetic material, which is available for fertilisation. If there is no separation of the homologous chromosomes (meiosis I) or no separation of the sister chromatids (meiosis II), there are two chromatids in the germ cell.
If this egg cell is fertilised, the cell has a total of three chromatids and this is called trisomy. Structural chromosomal aberrations are not caused by the divisions of meiosis. In this type of chromosomal aberration, the chromosome set consists of the desired 23 homologous chromosome pairs, but individual chromosomes have an altered structure.
This aberration can be, for example, gene mutations already described above: The cause of these aberrations is usually an incorrect crossing over during meiosis. The second cause may be an incorrect repair of double-strand breaks in the genetic material. This could also be interesting for you: Nuclear division
- Deletion (a piece of the chromosome is missing)
- Duplication (one piece of the chromosome is duplicated)
- Translocation (a part of a chromosome has been incorporated into another chromosome)
What is the chromosome aberration test?
There are various tests that can be used to detect chromosomal aberrations in the unborn child. However, there are also so-called in vitro and in vivo chromosomal aberration tests, which are used in toxicology. In vitro chromosome aberration test In the in vitro chromosome aberration test, a cell culture is treated with a certain substance that is suspected of causing chromosomal aberrations.
The cell culture consists of cells derived from mammals. Examples include cells from mice or lymphocytes from human blood. These cells are first cultivated so that they grow under optimal conditions.
Next, they are treated with the substance under investigation. This can be a dissolved substance, for example, which is added to the cell culture. After a certain exposure time, the cells are then examined under the microscope.
The chromosomes in the metaphase in particular are looked at and checked for changes. It is also useful to prepare a control culture that has not been treated with the test substance. This control allows the chromosome sets to be compared more easily.
In vivo chromosome aberration test The in vivo chromosome aberration test is similar to the in vitro test except that the test substance is introduced directly into the bone marrow of the living mammal. This creates realistic conditions, as the substance is present in the organism. Here too, the chromosome set is examined for abnormalities.
Using these two methods, substances can be tested for their mutagenic effect. There are various tests that can be used to examine chromosomal aberrations. On the one hand, there are tests that can be used to test whether a substance (e.g. nicotine) triggers chromosomal aberrations and thus increases the chance of cancer.
These tests are called in-vitro and in-vivo chromosomal aberration tests and are carried out by toxicologists. However, there are also tests that can be done in pregnant women to check whether the unborn child has a chromosomal aberration. There are several possibilities.
The first possibility is chromosome analysis, which is still the gold standard today. For example, amniotic fluid or umbilical cord blood can be used as examination material. Both numerical and structural chromosomal aberrations can be diagnosed under the microscope.
The second option would be a simple ultrasound, which can often detect chromosomal alterations. A sign of a chromosomal abnormality is, among other things, the absence of the nasal bone. Another test which takes less time than the chromosome analysis (duration: approx.
several days) is the FISH test (duration: maximum 2 days). The FISH test (fluorescence in situ hybridization test) can be used to display the chromosomes 13, 18, 21 and the X and Y chromosomes in fetal material (e.g. amniotic fluid) in color. A numerical chromosomal aberration can thus be determined by easy counting.
