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X-chromosome (ChrX) genotyping can complete the analysis of autosomal (AS) and Y-chromosomal (ChrY) markers very efficiently, especially in complex kinship testing cases.

These insights, which arose in the late nineties and in the first years of the current decade, increasingly induced investigations on ChrX markers for forensic use. Unlike forensic autosomal STRs and Y-chromosomal STRs, ChrX markers are so far only poorly reviewed in the world wide web (Introduction to forensic-ChrX-research).

This website aims to provide a database for ChrX STRs and ChrX STR haplotypes comprising published population data for populations from several countries. However, we do not claim to present a complete literature review.

This page mainly contains data, which have been published in peer reviewed scientific journals. However, scientists can submit data on population samples of interest, if the quality requirements are met. Decision making regarding publication is reserved for the forensic ChrX research board. The course of law is excluded.

In contrast to ChrY markers, which do not recombine during meiosis, the genetic localisation is an important issue for AS markers and ChrX markers when used in kinship testing. Since all ChrX markers are located on the same chromosome within an area of 240cM, working with these markers requires an exact knowledge about their genetic localisation. On this website, genetic location of established forensic markers is displayed on the ChrX STR linkage table and on the ChrX idiogram.

In kinship testing, typing of ChrX STR clusters provides a powerful tool, if the arrangement of STR alleles in the linked STRs can be allocated to haplotypes. With the very rare exception of males showing the Klinefelter syndrome, this applies to the male sex always. In addition, pedigree analyses frequently enable estimating the haplotypes of female individuals, too. Thus, we present haplotype frequencies of several populations for selected STR clusters. Please keep in mind, that very closely linked markers regularly exhibit a linkage disequilibrium. Hence, frequencies of haplotypes cannot be calculated by multiplicating the frequencies single alleles of the haplotypes involved but they must be estimated by the analysis of population samples.

Due to some special genetic properties of the ChrX, ethical problems during the ChrX typing may arise in some rare cases. Some remarks at the ‘Ethical considerations’ section can help to avoid critical situations.

To learn more about our website, please click on ‘Introduction to forensic-ChrX-research’.