Loss of the copy of a gene from one parent in a diploid organism
An example of loss of heterozygosity over time, in bottlenecking population. Different alleles painted in different colors. A diploid population of 10 individuals, that bottlenecked down to three individuals repeatedly, resulted in all individuals homozygous.
In genetics, loss of heterozygosity (LOH) is a type of genetic abnormality in diploid organisms in which one copy of an entire gene and its surrounding chromosomal region are lost.[1] Since diploid cells have two copies of their genes, one from each parent, a single copy of the lost gene still remains when this happens, but any heterozygosity (slight differences between the versions of the gene inherited from each parent) is no longer present.
^[Association of the autoimmune diseases scleroderma with an immunologic response to cancer,] Christine G. Joseph et al., Science, 343:152 (10 January 2014)