Application of X chromosomal STR polymorphisms to individual identification

The human DNA markers most commonly utilized in individual identification are autosomal short tandem repeat (STR), followed by Y-chromosome STRs and mitochondrial DNA. X-chromosomal short tandem repeat (X-STR) loci may efficiently complement autosomal markers in paternity testing, especially in deficient paternity cases with female offspring, and in kinship analysis involving large and incomplete pedigrees. X-STR loci are located on the non-recombining region of the X chromosome and are inherited as a block of linked haplotypes. Due to its unique inheritance pattern, the X chromosome is a potential candidate for forensic and human identity testing applications. Currently, more than 40 X-STRs have been established as forensic markers, and a large number of population data have been published. X-STR haplotyping can be of particular help in kinship testing in deficient paternity cases where a DNA sample from one of the parents is not available for testing. The ideal technique for X-STR typing is multiplex PCR, because as the number of polymorphic loci examined increases, the probability of identical alleles being present in two different individuals decreases. Multiplex systems have been developed in order to apply X-STRs efficiently for paternity testing. In view of the wide application of these markers, several X-STRs multiplex PCR systems have been validated for individual identification, which include four to thirty markers. Multiplex with greater number of markers are being developed to obtain a high degree of discrimination. Samples from a mass disaster site or from a crime scene exposed to environment are often not only highly degraded but also in very scarce quantities, making it difficult for scientists to perform multiple PCR analyses. Analysis of degraded DNA samples using mini X-STR multiplex systems will offer high efficacy for personal identification.