Loss of heterozygosity
From Biocrawler, the free encyclopedia.
Loss of heterozygosity in a cell represents the loss of a single parent's contribution to part of its genome. A common occurrence in cancer, it often indicates the presence of tumor suppressor gene in the lost region. Often, the remaining copy of the tumor suppressor gene will be inactivated by a point mutation. The canonical example is hereditary retinoblastoma, in which a single parent's contribution of the tumor suppressor Rb1 is flawed. Although most cells will have a functional second copy, chance loss of heterozygosity events in individual cells almost invariably lead to the development of this retinal cancer in the young child.
Loss of heterozygosity can arise by two methods. In the first, a region of a chromosome is deleted, resulting in only one copy remaining. In the second, genetic recombination leaves the cell with two copies of the chromosomal region, but both come from the same parent.
Loss of heterozygosity can be identified in cancers by noting the presence of heterozygosity at a genetic locus in an organism's germline DNA, and the absence of heterozygosity at that locus in the cancer cells. This is often done using polymorphic markers, such as microsatellites or single nucleotide polymorphisms, for which the two parents contributed different alleles.
