Research article
Population data for six X-chromosome STR loci in a Rio de Janeiro (Brazil) sample: Usefulness in forensic casework

https://doi.org/10.1016/j.fsigss.2007.10.100Get rights and content

Abstract

This study presents data for the X-chromosome STR loci DXS7133, DXS7424, DXS8378, DXS6807, DXS7423 and DXS8377. In order to establish a database, unrelated individuals (males and females) from Rio de Janeiro were typed for the above loci. No significant differences were observed between allele frequencies in male and female samples (non-differentiation exact P values  0.156). Hardy–Weinberg equilibrium was tested in the female sample and no significant deviations were found. All six markers have shown to be highly polymorphic in our sample with gene diversities varying between 0.6797 for DXS7133, and 0.9260 for DXS8377. Pairwise linkage disequilibrium analysis did not allow discharging a possible association between DXS7133 and DXS7424 alleles in Rio de Janeiro population. Parameters of forensic interest, like PDM, PDF, Hetobs, Hetexp, were calculated for each locus. The high discrimination power estimated in both males and females, as well as mean exclusion chance in father/daughter duos and in father/mother/daughter trios, demonstrates the usefulness of these six markers in forensic investigation.

Introduction

X-chromosome STR markers have been used in supplementation to autosomal and Y-chromosomal STRs markers in forensic analysis [1]. They can be used to establish kinship, especially in deficiency of paternity cases when female descendents are under investigation. Men transmit to his daughters one X-chromosome they received from their mothers. Therefore, in the absence of the father, paternal grandmother and uncles can be used to infer the father's profile. In these cases, we can also use the information obtained from sisters and half-sisters who share the X-chromosome haplotypes with females under investigation. X-STRs tend to present a mean exclusion chance higher than that of autosomal STRs [2].

The aim of this study was to describe the polymorphism of six X-chromosome STR loci, involving three X-chromosome linkage groups I, II and IV (DXS7133, DXS7424, DXS8378, DXS6807, DXS7423 and DXS8377) in Rio de Janeiro population. DXS8377 revealed to be the most polymorphic among these markers.

In order to evaluate the usefulness and potential applications of these six X-chromosome markers in forensic practice we perform HWE and LD tests, as well as genetic comparison of the two female and male samples. Statistical parameters with forensic relevance were calculated, such as PDF, PDM, PIC, MEC.

Section snippets

Materials and methods

Blood samples were collected from individuals living in Rio de Janeiro, Brazil. A total of 263 unrelated healthy donors (129 males and 134 females) were typed for DXS7133, DXS7424 and DXS8378 and 213 individuals (94 males and 119 females) for DXS6807, DXS7423 and DXS8377.

DNA was extracted using salting out method described by Miller et al. [3].

Multiplexes PCR reactions were performed using primers described by Poetsch et al. [4]. Primers were fluorescent labeled with fluorescein or hexamethyl

Results and discussion

A Brazilian population sample of genetically unrelated individuals was studied for six X-chromosome markers: DXS7133, DXS7424, DXS8378, DXS6807, DXS7423 and DXS8377. Exact test of differentiation based on allele frequencies show no significant differences (P = 0.431 for DXS7133, P = 0.773 for DXS7424, P = 0.193 for DXS8378, P = 0.157 for DXS6807, P = 0.379 for DXS 7423 and P = 0.329 for DXS8377) between female and male samples. In view of this, samples were pooled and allele frequencies are presented in

Funding source

FAPERJ – Rio de Janeiro Government for Scientific Research Agency. The sponsor had no involvement in the development of the paper or decisions related to the paper.

Conflict of interest

None.

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