page_title: Loss of heterozygosity
hierarchical_section_title: Loss of heterozygosity
caption_attribution_description: English: Loss of heterozygosity over time in a bottlenecking population. A diploid population of 10 individuals, that bottlenecks down to three individuals repeatedly. In the first generation I colour every allele a different colour so we can track their descendants, there are no new mutations.
context_page_description: Loss of heterozygosity is a cross chromosomal event that results in loss of the entire gene and the surrounding chromosomal region.
  All diploid cells, for example most human somatic cells, contain two copies of the genome, one from each parent; each human copy contains approximately 3 billion bases. For the majority of positions in the genome the base present is consistent between individuals, however a small percentage may contain different bases and these positions are called single nucleotide polymorphisms or SNPs. When the genomic copies derived from each parent have different bases for these polymorphic regions the region is said to be heterozygous. Most of the chromosomes within somatic cells of individuals are paired, allowing for SNP locations to be potentially heterozygous. However, one parental copy of a region can sometimes be lost, which results in the region having just one copy. The single copy cannot be heterozygous at SNP locations and therefore the region shows loss of heterozygosity. Loss of heterozygosity due to loss of one parental copy in a region is also called hemizygosity in that region.
context_section_description: Loss of heterozygosity (LOH) is a cross chromosomal event that results in loss of the entire gene and the surrounding chromosomal region.
  All diploid cells, for example most human somatic cells, contain two copies of the genome, one from each parent (chromosome pair); each human copy contains approximately 3 billion bases (adenine (A), guanine (G), cytosine (C) or thymine (T)). For the majority of positions in the genome the base present is consistent between individuals, however a small percentage may contain different bases (usually one of two; for instance, ‘A’ or ‘G’) and these positions are called single nucleotide polymorphisms or SNPs. When the genomic copies derived from each parent have different bases for these polymorphic regions (SNPs) the region is said to be heterozygous. Most of the chromosomes within somatic cells of individuals are paired, allowing for SNP locations to be potentially heterozygous. However, one parental copy of a region can sometimes be lost, which results in the region having just one copy. The single copy cannot be heterozygous at SNP locations and therefore the region shows loss of heterozygosity (LOH). Loss of heterozygosity due to loss of one parental copy in a region is also called hemizygosity in that region.
caption: 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.
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