Forensic Applications of Markers Present on the X Chromosome

Abstract

Microsatellite genetic markers are the gold standard for human genetic identification. Forensic analyses around the world are carried out through protocols using the analysis of STR markers in autosomal chromosomes and in the Y chromosome to solve crimes. However, these analyses do not allow for the resolution of all cases, such as rape situations with suspicion of incest, paternity without a maternal sample for comparison, and biological traces with DNA mixture where the profile sought is female, among other situations. In these complex cases, the study of X-chromosome STR markers significantly increases the probability of identification by complementing the data obtained for autosomal and Y-chromosome markers, due to the unique structure of the X chromosome and its exclusive method of inheritance. However, there are currently no validated Brazilian protocols for this purpose, nor are there any population data necessary for statistical analyses that must be included in the issuance of expert reports. Thus, the aim of this article is to provide a literary review of the applications of X-chromosomal markers in population genetics.

Recombulator-X: a fast and user-friendly tool for estimating X chromosome recombination rates in forensic genetics

“…The proper biostatistical evaluation of the evidential weight in personal identification and kinship tests when dealing with X chromosome markers is a nagging problem in forensics, due to physical linkage [3,6,46,50,63]. Despite being crucial for unbiased formulations of the evidential weight, as also highlighted by the International Society of Forensic Genetics [6], few biostatistical tools for the evaluation of recombination rates between adjacent forensic markers along the X chromosome are available today.…”

Recent advances in forensic biology and forensic DNA typing: INTERPOL review 2019–2022

“…A 20-year review of X-chromosome use in forensic genetics examined the number and types of markers available, an overview of worldwide population data, the use of X-chromosome markers in complex kinship testing, mutation studies, current weaknesses, and future prospects [ 502 ]. One example of the forensic application of X-chromosome markers include use in relationship testing cases involving suspicion of incest or paternity without a maternal sample for comparison [ 503 ]. Four new X-STR multiplex assays were described along with validation studies including a 19plex [ 504 ], a 16plex [ 505 ], another 19plex – the Microreader 19X Direct ID System [ 506 ], and an 18plex named TYPER-X19 multiplex assay [ 507 ].…”

The Skeletal Remains of Soldiers from the Two World Wars: Between Identification, Health Research and Memorial Issues

“…The most common method used is genetic identification by STR profile comparison: STR (short tandem repeat) markers are amplified and compared to one another [ 8 ]. Regarding STR marker choice, chromosome-X-STR markers tend to be more stable than Y-STR and provide better quality for identification [ 27 ]. As DNA tends to degrade with time [ 28 ], simple DNA comparisons are not always feasible: Y-STR analysis (Y chromosome, paternal lineage) and the analysis of other nuclear DNA cannot be performed in this case [ 3 ].…”