loss of heterozygosity

Loss of heterozygosity is one common way a cell loses its genetic backup. Imagine you keep two copies of an important key, one already worn down and unreliable, the other still good. Loss of heterozygosity is the moment you lose the good copy and are left holding only the faulty one.

Heterozygous means a cell has two different versions of a gene at a locus, one from each parent. Loss of heterozygosity, often abbreviated LOH, is when a cell that started with two different alleles ends up with only one kind, because the other allele is deleted or replaced. This can occur through chromosome loss, large deletions, or recombination that copies one allele over the other.

In cancer, loss of heterozygosity is a classic mechanism for the second hit on a tumor-suppressor gene: a cell that inherited one broken allele loses the remaining good allele and is left with no working protection. Detecting LOH across a tumor's genome helps researchers locate tumor suppressors and trace which protective genes have been silenced.