Gene

Gene is the basic unit of heredity. A gene is a specific section on the DNA of a chromosome or the DNA present in mitochondria, plastids and plasmids, which codes for certain hereditary structures or functions of an organism. The gene thus represents the smallest functional unit in the genome of an organism. As a rule, each gene occupies a specific location on the chromosome, which is referred to as the gene locus.

However, there are also examples of genes consisting of several regions distributed on a chromosome. For example, the genes coding for antibodies are only assembled into a functional unit during the differentiation of the cell.

Genes that occupy the corresponding gene loci on homologous chromosomes are referred to as allelic genes (abbreviated, but incorrectly, as "alleles"). They can be completely identical in terms of their genetic information. In this case, the gene locus is referred to as homozygous.

However, genes can also be different from each other. In this case, the gene locus for the allele pair in question is referred to as heterozygous. If one state form of a gene, i.e. one allele, covers the state form of another allele in its expression of a characteristic, this is referred to as a dominant versus a recessive allele.

The totality of an organism's genes in their respective identical or different state forms is referred to as the genotype. A gene map represents the linear arrangement of genes in the genome of an organism. Numerous genodermatoses have now been mapped (assigned to a gene map) and clarified using molecular biology.