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The remaining copy of the tumor suppressor gene can be inactivated by a point mutation or via other mechanisms, resulting in a loss of heterozygosity event, and leaving no tumor suppressor gene to protect the body. Loss of heterozygosity does not imply a homozygous state (which would require the presence of two identical alleles in the cell).
The measures F IS, F ST, and F IT are related to the amounts of heterozygosity at various levels of population structure. Together, they are called F-statistics, and are derived from F, the inbreeding coefficient. In a simple two-allele system with inbreeding, the genotypic frequencies are:
SNPs can also be used to study genetic abnormalities in cancer. For example, SNP arrays can be used to study loss of heterozygosity (LOH). LOH occurs when one allele of a gene is mutated in a deleterious way and the normally-functioning allele is lost. LOH occurs commonly in oncogenesis.
The wing-spot test in D. melanogaster was first described by Graf and Würgler. [3] The wing-spot test determines for the induction of mutant spots that represent the loss of heterozygozity due to point mutation, deletion, nondisjunction, or mitotic recombination using the recessive genetic markers multiple wing hair (mwh) and flare-3 (flr3), located on chromosome number 3.
In a cohort of 96 patients with pancreatic cancers, 6 cases were known to have mutation or allele loss and 11 (11.5%) patients were identified by HRDetect to an exceed cutoff of 0.7. The study observed a similar result of sensitivity approaching 100%, with five other cases identified.
A loss in heterozygosity refers to the loss of one of two versions—or alleles—of a gene. If one of the lost alleles helps to suppress tumors, like the gene for the retinoblastoma protein for example, then the loss of heterozygosity can lead to cancer. [107]: 1236
A significantly lower proportion of HLA-DRB1 heterozygosity exists among HCV-infected cases than uninfected cases. The differences were more pronounced with alleles represented as functional supertypes (P = 1.05 × 10 −6 ) than those represented as low-resolution genotypes (P = 1.99 × 10 −3 ).
In medical genetics, compound heterozygosity is the condition of having two or more heterogeneous recessive alleles at a particular locus that can cause genetic disease in a heterozygous state; that is, an organism is a compound heterozygote when it has two recessive alleles for the same gene, but with those two alleles being different from each other (for example, both alleles might be ...