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Analysis of linkage and linkage disequilibrium for eight X-STR markers.
Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Health Sciences.
Mathematical Sciences, Chalmers University of Technology, and Mathematical Sciences Göteborg University, Göteborg, Sweden.
Department of Medical Genetics, Ullevaal University Hospital, Oslo, Norway.
Linköping University, Department of Clinical and Experimental Medicine, Forensic Genetics . Linköping University, Faculty of Health Sciences.
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2008 (English)In: Forensic science international. Genetics, ISSN 1878-0326, Vol. 3, no 1, 37-41 p.Article in journal (Refereed) Published
Abstract [en]

X-chromosomal short tandem repeats (X-STR) have proven to be informative and useful in complex relationship testing. The main feature of X-STR markers, compared to autosomal forensic markers, is that all loci are located on the same chromosome. Thus, linkage and linkage disequilibrium may occur. The aim of this work was to study population genetic parameters of eight X-STR markers, located in four linkage groups. We present haplotype frequencies, based on 718 Swedish males, for the four linkage groups included in the Argus X-8 kit. Forensic efficiency parameters have been calculated as well as the allelic association between the tested markers for detection of linkage disequilibrium. To study the occurrences of recombination between the loci, both Swedish and Somali families were typed. A mathematical model for the estimation of recombination frequencies is presented and applied on the family samples. Our study showed that the tested markers all have highly informative forensic values and that there is a significant degree of linkage disequilibrium between the STR markers within the four linkage groups. Furthermore, based on the tested families, we also demonstrated that two of the linkage groups are partially linked. A consequence of these findings is that both linkage and linkage disequilibrium should be accounted for when producing likelihood ratios in relationship testing with X-STR markers.

Place, publisher, year, edition, pages
Elsevier , 2008. Vol. 3, no 1, 37-41 p.
Keyword [es]
X-chromosomal STR, Linkage, Linkage disequilibrium, Recombination, Likelihood ratios, Sweden
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-54740DOI: 10.1016/j.fsigen.2008.09.006PubMedID: 19083865OAI: diva2:309696
Available from: 2010-04-08 Created: 2010-04-08 Last updated: 2010-04-09
In thesis
1. Populations and Statistics in Forensic Genetics
Open this publication in new window or tab >>Populations and Statistics in Forensic Genetics
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

DNA has become a powerful forensic tool for solving cases such as linking a suspect to a crime scene, resolving biological relationship issues and identifying disaster victims. Traditionally, DNA investigations mainly involve two steps; the establishment of DNA profiles from biological samples and the interpreta-tion of the evidential weight given by theses DNA profiles. This thesis deals with the latter, with focus on models for assessing the weight of evidence and the study of parameters affecting these probability figures.

In order to calculate the correct representative weight of DNA evidence, prior knowledge about the DNA markers for a relevant population sample is required. Important properties that should be studied are, for example, how frequently certain DNA-variants (i.e. alleles) occur in the population, the differences in such frequencies between subpopulations, expected inheritance patterns of the DNA markers within a family and the forensic efficiency of the DNA markers in casework.

In this thesis we aimed to study important population genetic parameters that influence the weight of evidence given by a DNA-analysis, as well as models for proper consideration of such parameters when calculating the weight of evi-dence in relationship testing.

We have established a Swedish frequency database for mitochondrial DNA haplotypes and a haplotype frequency database for markers located on the X-chromosome. Furthermore, mtDNA haplotype frequencies were used to study the genetic variation within Sweden, and between Swedish and other European populations. No genetic substructure was found in Sweden, but strong similari-ties with other western European populations were observed.

Genetic properties such as linkage and linkage disequilibrium could be im-portant when using X-chromosomal markers in relationship testing. This was true for the set of markers that we studied. In order to account for this, we pro-posed a model for how to take linkage and linkage disequilibrium into account when calculating the weight of evidence provided by X-chromosomal analysis.

Finally, we investigated the risk of erroneous decisions when using DNA in-vestigations for family reunification. We showed that the risk is increased due to uncertainties regarding population allele frequencies, consanguinity and compet-ing close relationship between the tested individuals. Additional information and the use of a refined model for the alternative hypotheses reduced the risk of making erroneous decisions.

In summary, as a result of the work on this thesis, we can use mitochondrial DNA and X-chromosome markers in order to resolve complex relationship in-vestigations. Moreover, the reliability of likelihood estimates has been increased by the development of models and the study of relevant parameters affecting probability calculations.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 55 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1175
National Category
Medical and Health Sciences
urn:nbn:se:liu:diva-54742 (URN)978-91-7393-420-6 (ISBN)
Public defence
2010-05-07, Elsa Brändström-salen, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Available from: 2010-04-08 Created: 2010-04-08 Last updated: 2010-04-08Bibliographically approved

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