Spanish allele and haplotype database for 32 X-chromosome Insertion-Deletion polymorphisms

Abstract

X-chromosome markers have been proved to be decisive both complementing and solving kinship analysis, particularly when autosomal markers are not able to produce adequate likelihood ratios between different hypothesis. On the other hand, Pereira et al., (2012) have demonstrated that 32 Insertion/Deletion (InDel) markers located on the X-Chromosome have a very important power of discrimination in human populations, being a novel tool in the forensic and population fields. So, the aim of the present work was testing the forensic and population genetic efficiency of the 32 X-InDel polymorphisms in the Spanish population, and subsequently build an allele/haplotype frequencies database.

To accomplish this objective, a total of 555 samples comprising male individuals from 13 Spanish regions were analysed for the above mentioned 32 X-InDels in two independent laboratories. A pairwise FST analysis was performed in order to understand if the studied Spanish sub-populations present significant differences among them, detecting possible population substructure. Also, linkage disequilibrium analyses were computed to investigate the presence of association between markers in the Spanish population.

After Bonferroni correction, the absence of significant differences among the studied regions supports a global Spanish population database. Concerning LD, besides previously reported linked markers MID356-MID357 and MID3690-MID3719-MID2089, we also detected significant association between MID3703-MID3774, even after Bonferroni correction.

Finally, after computing allele and haplotype frequencies, forensic efficiency parameters were calculated (PDmales = 99.999976 %; PDfemales = 99.99999999998 %). Mean exclusion chance values for duos were 0.999 and trios 0.99999. These results reinforce the suitability of the 32 X-InDels marker set both in identification and kinship studies.