Genetic testing (synonyms: DNA analysis, also DNA test, DNA analysis, DNA test, gene analysis, genome analysis) refers to molecular biological procedures that examine DNA (German abbreviation DNS: deoxyribonucleic acid) in order to draw conclusions about various genetic aspects of an individual. In the meantime, more than 3,000 monogenic diseases (monogenic diseases, “single-gene disease”) have been molecularly characterized, which can be examined by means of DNA analysis. Characteristic of monogenic diseases (monogenetic diseases) is that their inheritance pattern usually follows Mendelian rules. Numerous genetic diseases are based on an interaction of several defective genes. These are called polygenic diseases (polygenetic diseases). While the entire genome is analyzed in a genome analysis, a genetic test based on a SNP (see below) or STR (see below) detects a risk for a single disease (= predisposition to a disease) or trait. Furthermore, it can be used to determine relationships between two individuals as well as certain traits (e.g. a characteristic smell of urine is perceived after eating asparagus). If only potentially coding genes are analyzed in a genome analysis, this is referred to as an exome analysis. In the past, only chromosome analysis was available for suspected genetic diseases. This involves the preparation of a so-called karyogram. This is the ordered representation of the individual chromosomes of a cell photographed through a microscope. All chromosomes of a cell are sorted according to morphological aspects (size, centromere position, banding pattern). Chromosomes contain the genetic material of a human being. A human being has 46 chromosomes. The chromosome pairs 1-22 are the autosomes, the 23rd chromosome pair are the sex chromosomes (gonosomes; XY in man and XX in woman). The totality of the material carriers of the heritable information of a cell is called the genome. On the chromosomes are the genes, these represent a section on the DNA (deoxyribonucleic acid). Their physical location is called the gene locus (gene locus). Specific genes have specific tasks. Every person has the same genes, but what ultimately makes them different are the different variations of base pairs, which are called SNPs (single nucleotide polymorphism; see SNPedia below). Thus, although every human being has the same SNPs, their “nucleic bases” (and ultimately base pairs) in a DNA strand can be different. Thus, the possible nucleic bases in DNA are: adenine, guanine, thymine, and cytosine, which are abbreviated as A, G, T, and C, respectively. In a genetic test/DNA test, the SNPs are genotyped and the individually different nucleic bases are determined. In chromosomes 1-21 there are always two variations of nucleic bases, one from the mother and one from the father. Females, since they have two X chromosomes, also have two variations of nucleic bases in SNPs of the X chromosome. Since males have one X chromosome and one Y chromosome, they have only one nucleic base in both SNPs in the X chromosome and SNPs in the Y chromosome. However, some DNA tests e.g. FTDNA (Family Tree DNA) do not test the SNPs but the so-called STRs (Short tandem repeat). Here, attention is paid to certain repetition patterns with regard to the base pairs in a DNA strand. This is particularly helpful where patterns play a major role. This is used, for example, in determining ancestral composition, mitochondrial haplogroup and Y-haplogroup. However, STRs analysis is not useful for determining disease risk. Here, the SNP(s) associated with disease risk must be analyzed. Today, genome analysis or genetic testing is increasingly used for genetic diagnosis. For example, genetic tests are used to detect the following genetic diseases: Cystic Fibrosis (CFTR gene), Hereditary Colorectal Carcinoma without Polyposis (occurrence of numerous polyps) (HNPCC gene), and Breast Cancer (breast cancer; BRCA genes). Testing for BRCA1/2, for example, is increasingly being replaced by panel testing in the USA; in some cases, up to 90 cancer– and breast cancer-associated gene variants are examined. Examples of genetic tests available in Germany:
- 23andme (a test with about 600,000 SNPs, which gives an overview of the ancestral composition, among other things.
- AncestryDNA (Relates to health aspects).
- MyHeritage DNA (cheapest DNA test with genealogical analysis).
- IGenea (DNA test with genealogical analysis).
- Living DNA (DNA test with detailed genealogical analysis).
- FTDNA (DNA test for genealogy that provides a lot of information about mitochondrial DNA and about the Y chromosome, depending on the version).
