The absence of one copy (allele) of a gene or of part of one copy of a chromosome. In some circumstances, this may imply the presence of a tumour suppressor gene in the lost genetic material.

(synonym: LOH) At a particular locus heterozygous for a deleterious mutant allele and a normal allele, a deletion or other mutational event within the normal allele renders the cell either hemizygous (one deleterious allele and one deleted allele) or homozygous for the deleterious allele Related Terms: deletion ; hemizygous ; heterozygote ; homozygote

In cancer, loss of a second allele of a gene when the first allele is already altered or lost

only a single allele of a gene is present in a cell when previously two distinguishable alleles had been present

e-LOH is a statistical methodology that utilizes single nucleotide polymorphisms as markers to identify the loss of a missing gene. By comparing the ratio of maternal DNA to paternal DNA, one may be able to identify chromosomal loss that may be associated with many cancers.

Loss of heterozygosity (LOH) in a cell represents the loss of one parent's contribution to part of the cell's 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 had been inactivated by a point mutation.