Principle : Cytogenetics is the study of the chromosomes of an individual (fetus, child or adult) from a collection made either by post-natal (venous blood, skin biopsy), or by prenatal (amniotic fluid, fetal blood, chorionic villi).
For the study of chromosomes, two distinct technologies can be used :
a – conventional cytogenetics (karyotyping) that provides a rendering result with a definition of the order of 3mb (megabase).
b – the molecular cytogenetics (fish), which allows a targeted study with a definition of the order of 1 kb (kilobase).
Cytogenetics, molecular is a use of the specificity of the pairing base to the base of the molecule of dna for clear identification of a whole chromosome or even a single fragment.
The principle is based on the use of a molecular probe, that is to say, a small sequence of dna (or rna ) whose normal location is known in the genome and is characterized chemically so that it can be identified by the following. this probe is brought into contact with the chromosomes of mitosis (or interphase nuclei) and will hybridize (attach) specifically at the level of its complementary sequence. we can then visualize the probe in the microscope, the location of which precisely identifies the chromosomal region to which it is complementary.
The probes are labeled either with a fluorescent molecule, or a hapten (a molecule that can be recognized by an antibody). in the first case, the probe is directly visible in the fluorescence microscope, while in the latter, an additional step of revelation with an antibody fluorescent is necessary.