Topic
Loss of heterozygosity
About: Loss of heterozygosity is a research topic. Over the lifetime, 10247 publications have been published within this topic receiving 537539 citations.
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TL;DR: It is shown that the number of individuals to be used for estimating average heterozygosity can be very small if a large number of loci are studied and the average heter homozygosity is low.
Abstract: The magnitudes of the systematic biases involved in sample heterozygosity and sample genetic distances are evaluated, and formulae for obtaining unbiased estimates of average heterozygosity and genetic distance are developed. It is also shown that the number of individuals to be used for estimating average heterozygosity can be very small if a large number of loci are studied and the average heterozygosity is low. The number of individuals to be used for estimating genetic distance can also be very small if the genetic distance is large and the average heterozygosity of the two species compared is low.
11,137 citations
TL;DR: A method is presented by which the gene diversity (heterozygosity) of a subdivided population can be analyzed into its components, i.e., the gene diversities within and between subpopulations.
Abstract: A method is presented by which the gene diversity (heterozygosity) of a subdivided population can be analyzed into its components, i.e., the gene diversities within and between subpopulations. This method is applicable to any population without regard to the number of alleles per locus, the pattern of evolutionary forces such as mutation, selection, and migration, and the reproductive method of the organism used. Measures of the absolute and relative magnitudes of gene differentiation among subpopulations are also proposed.
8,465 citations
TL;DR: In this article, two statistical tests for detecting a heterozygosity excess are described, and the most useful markers for bottleneck detection are those evolving under the infinite allele model (IAM) and they provide guidelines for selecting sample sizes of individuals and loci.
Abstract: When a population experiences a reduction of its effective size, it generally develops a heterozygosity excess at selectively neutral loci, i.e., the heterozygosity computed from a sample of genes is larger than the heterozygosity expected from the number of alleles found in the sample if the population were at mutation drift equilibrium. The heterozygosity excess persists only a certain number of generations until a new equilibrium is established. Two statistical tests for detecting a heterozygosity excess are described. They require measurements of the number of alleles and heterozygosity at each of several loci from a population sample. The first test determines if the proportion of loci with heterozygosity excess is significantly larger than expected at equilibrium. The second test establishes if the average of standardized differences between observed and expected heterozygosities is significantly different from zero. Type I and II errors have been evaluated by computer simulations, varying sample size, number of loci, bottleneck size, time elapsed since the beginning of the bottleneck and level of variability of loci. These analyses show that the most useful markers for bottleneck detection are those evolving under the infinite allele model (IAM) and they provide guidelines for selecting sample sizes of individuals and loci. The usefulness of these tests for conservation biology is discussed.
4,106 citations
TL;DR: Colorectal tumor DNA was examined for somatic instability at (CA)n repeats on human chromosomes 5q, 15q, 17p, and 18q, and this instability was significantly correlated with the tumor's location in the proximal colon and with increased patient survival and loss of heterozygosity.
Abstract: Colorectal tumor DNA was examined for somatic instability at (CA)n repeats on human chromosomes 5q, 15q, 17p, and 18q. Differences between tumor and normal DNA were detected in 25 of the 90 (28 percent) tumors examined. This instability appeared as either a substantial change in repeat length (often heterogeneous in nature) or a minor change (typically two base pairs). Microsatellite instability was significantly correlated with the tumor's location in the proximal colon (P = 0.003), with increased patient survival (P = 0.02), and, inversely, with loss of heterozygosity for chromosomes 5q, 17p, and 18q. These data suggest that some colorectal cancers may arise through a mechanism that does not necessarily involve loss of heterozygosity.
3,093 citations
TL;DR: Molecular features of "familial" cancers were compared with those of sporadic colon cancers, and a mechanism for familial tumorigenesis different from that mediated by classic tumor suppressor genes is suggested.
Abstract: A predisposition to colorectal cancer is shown to be linked to markers on chromosome 2 in some families. Molecular features of "familial" cancers were compared with those of sporadic colon cancers. Neither the familial nor sporadic cancers showed loss of heterozygosity for chromosome 2 markers, and the incidence of mutations in KRAS, P53, and APC was similar in the two groups of tumors. Most of the familial cancers, however, had widespread alterations in short repeated DNA sequences, suggesting that numerous replication errors had occurred during tumor development. Thirteen percent of sporadic cancers had identical abnormalities and these cancers shared biologic properties with the familial cases. These data suggest a mechanism for familial tumorigenesis different from that mediated by classic tumor suppressor genes.
2,717 citations