Currently, genetic analyses are used primarily in prenatal diagnostics, in preimplantation genetic diagnosis (PGD) – which is highly controversial and currently not permitted in Germany – in which an artificially fertilized embryo is examined for hereditary diseases and chromosomal abnormalities before implantation, and in preventive health care or genetic counseling for those who wish to have children. In this way, statistical probabilities for the development of some diseases can be predicted (e.g. for breast cancer in certain gene carriers) or for the passing on of a hereditary disease to the children. The following methods are used for this purpose:
- DNA sequencing: in principle, a number of different methods are used for this purpose, often based on the principle of cutting DNA into fragments with enzymes, artificially amplifying these fragments (often with the polymerase chain reaction = PCR) and then determining their lengths, or on looking for specific patterns in the DNA strands. The examined sections are then compared with those in healthy genes. Prenatal diagnostics also uses fluorescence in situ hybridization (FISH), in which the chromosomes in the cell nuclei are examined with specific probes coupled with a fluorescent dye. In this way, sex and changes in chromosomes regarding number or structure can be determined.
- Mapping of chromosomes: various methods are also suitable for this purpose. For example, the chromosomes in a cell can be photographed and sorted by microscope and staining according to structural aspects (karyogram). This can be used to determine the sex of an individual and to detect or exclude some hereditary diseases such as Down syndrome. Other methods of genetic research (e.g., pedigree analysis, linkage analysis) are also used to map and clarify questions, such as how a particular disease is inherited.
