Forensics

Weir, B. S.

doi:10.1002/9780470061619.ch43

Cited by 6 publications

(3 citation statements)

References 30 publications

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“…, n, where t ¼ nðn 1 1Þ=2]. The allele frequencies of a subpopulation were generated from the Dirichlet distribution using the parameter u and the allele frequencies of the entire population, as described in Weir (2003). The genotypes of two individuals with a given relationship, parent-offspring (PO), full-sib (FS), half-sib (HS), and unrelated (UR), are then generated at each of a number of marker loci using the allele frequencies of the subpopulation.…”

Section: Theory and Methodsmentioning

confidence: 99%

Unbiased Relatedness Estimation in Structured Populations

Wang

2011

Genetics

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Knowledge of the genetic relatedness between individuals is important in many research areas in quantitative genetics, conservation genetics, forensics, evolution, and ecology. In the absence of pedigree records, relatedness can be estimated from genetic marker data using a number of estimators. These estimators, however, make the critical assumption of a large random mating population without genetic structures. The assumption is frequently violated in the real world where geographic/social structures or nonrandom mating usually lead to genetic structures. In this study, I investigated two approaches to the estimation of relatedness between a pair of individuals from a subpopulation due to recent common ancestors (i.e., relatedness is defined and measured with the current focal subpopulation as reference). The indirect approach uses the allele frequencies of the entire population with and without accounting for the population structure, and the direct approach uses the allele frequencies of the current focal subpopulation. I found by simulations that currently widely applied relatedness estimators are upwardly biased under the indirect approach, but can be modified to become unbiased and more accurate by using Wright's F st to account for population structures. However, the modified unbiased estimators under the indirect approach are clearly inferior to the unmodified original estimators under the direct approach, even when small samples are used in estimating both allele frequencies and relatedness.K NOWING the degree of relatedness between individuals is essential in many research areas in quantitative genetics, conservation genetics, forensics, evolution, and ecology (Ritland 1996;Lynch and Ritland 1999;Weir et al. 2006). The expected value of relatedness between two individuals (e.g., 0.5 for parent-offspring in a large random mating population) can be easily calculated from their pedigree records. When pedigree is unavailable, incomplete, or unreliable, genetic marker information can be used instead to obtain an estimate of the realized value of relatedness, using a number of estimators developed for this purpose (e.g

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Section: Theory and Methodsmentioning

confidence: 99%

Unbiased Relatedness Estimation in Structured Populations

Wang

2011

Genetics

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“…Under the Dirichlet model, joint probabilities for sets of alleles can be calculated as described, for example, in Weir (2003). In particular, if (p 1 , p 2 , .…”

Section: Theory and Methodsmentioning

confidence: 99%

“…Each simulation began with the generation of allele frequencies for the overall population, and allele frequencies in the subpopulation were stochastically generated from these using the Dirichlet distribution as described, for example, in Weir (2003). In our analyses, we used the allele frequencies from the ancestral population in estimating the relatedness between individuals in subpopulations.…”

Section: Ibs Mode Allelic Statementioning

confidence: 99%

A Maximum-Likelihood Method for the Estimation of Pairwise Relatedness in Structured Populations

2007

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A maximum-likelihood estimator for pairwise relatedness is presented for the situation in which the individuals under consideration come from a large outbred subpopulation of the population for which allele frequencies are known. We demonstrate via simulations that a variety of commonly used estimators that do not take this kind of misspecification of allele frequencies into account will systematically overestimate the degree of relatedness between two individuals from a subpopulation. A maximum-likelihood estimator that includes F ST as a parameter is introduced with the goal of producing the relatedness estimates that would have been obtained if the subpopulation allele frequencies had been known. This estimator is shown to work quite well, even when the value of F ST is misspecified. Bootstrap confidence intervals are also examined and shown to exhibit close to nominal coverage when F ST is correctly specified. The above methods generally assume that allele frequencies are known without error, but Wang (2002) also considered the case in which allele frequencies were estimated from a sample of size N from the population in which relatedness is to be estimated. In this work, we consider a different situation: the case in which the individuals examined belong to a subpopulation of the population to which known allele frequencies apply. An example of this situation would be when ''European'' allele frequencies are used in estimating the relatedness between two individuals who happen to be Italian.The effect of using allele frequencies from the overall population is to shift the reference from which we measure relatedness back in time. As an illustration, consider the case in which two individuals share copies of an allele that is common in their subpopulation, but very rare in the population as a whole. Using the subpopulation allele frequencies, the fact that both individuals have this allele provides little evidence for relatedness. When the population allele frequencies are used, however, the evidence for relatedness becomes strong. The difference is that, when the population allele frequencies are used, relatedness is implicitly measured with respect to the time when the population allele frequencies held in the subpopulation, that is, before the subpopulation split from the ancestral population (which may be assumed to have allele frequencies similar to that of the current overall population-there is an implicit assumption here that the overall population is so large that its allele frequencies remain roughly unchanged over time). In this scenario, the relatedness estimate using the population allele frequencies is affected by the generations during which the allele frequencies in the subpopulation were diverging via drift from that in the overall population. From that perspective, the abundant copies of the allele in the subpopulation may all be copies of one allele in the ancestral population and these two individuals both have copies because they share common ancestry. Hence, even though the indiv...

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2015

Weight‐of‐Evidence for Forensic DNA Profiles

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Forensics

Cited by 6 publications

References 30 publications

Unbiased Relatedness Estimation in Structured Populations

Unbiased Relatedness Estimation in Structured Populations

A Maximum-Likelihood Method for the Estimation of Pairwise Relatedness in Structured Populations

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