SEX DETERMINATION IN FORENSIC ODONTOLOGY Identification of living beings and dead bodies is of great importance in Forensic science. Sex determination is one of the important steps in establishing identity. Sex identification in international sports: In 1932 Helen Stephens and Stella Walsh: Hitler’s Olympics In 1936 Stella accused Stephens of being male and so a crude physical examination including gross physical examination of external genitalia was done.
In 1966 gender identification became compulsory in the form of gynecological examination: nude parades – Irina and Tamara Press In 1968 Olympics, barr body detection was introduced and widely proclaimed to be the solution to gender misinterpretation in sports. This was the simpler, objective and more dignified test involving the cytological analysis of the buccal smear. First detected by Murray Barr in 1948 during research on the nervous system of cats – cells were analyzed following electrical stimulation and a dark body was found in the nucleus of certain animals.
This distinction was found to be related to sex & found in human autopsies as well. These nuclear findings came to be known as BARR BODY found associated with only XX sex chromosome, related to the chromatin clump which occurs due to the inactivation of the other paired sex chromosome. Ewa Klobukowska first polish sprinter to be disqualified following Barr Body examination. Created more problems than it solved. Gender identification purely via a chromosomal test failed to interpret the complexity of sex determination.
Females having complete androgen insensitivity syndrome were barred because of a XY chromosome inspite of complete female phenotype whereas those with Kleinfelter’s syndrome having XXY chromosome had an unfair advantage because of their physique. In 1991, Barr Body examination replaced by PCR for the SRY locus performed on DNA obtained from buccal smears. All women were screened from 1992 Olympics onwards. None were reported as deliberately misinterpreting the gender, although however it lead to embarrassment and controversy.
Therefore, from 1999, compulsory gender identification was withdrawn and was to be performed only when a suspicion was reported. DNA ANALYSIS: DNA PROFILING: AMEL gene: In forensic casework the human amelogenin gene, which is located on both the X and Y chromosome as single copies in the XY homologous regions, is widely used for sex determination by PCR in forensic routine analysis or anthropology Gender identification (sex-typing) is commonly performed in conjunction with STR typing kit using PCR products generated from the amelogenin gene that occurs on both the X- and Y-chromosome.
Since females are X,X, only a single peak is observed when testing female DNA whereas males, which possess both X and Y chromosomes, exhibit two peaks with a standard amelogenin test The ratio of amelogenin X and Y PCR products can be helpful in deciphering mixtures involving male and female DNA such as sexual assault evidence anomalous amelogenin results occur due to primer binding site mutations or deletions of sections of the Y-chromosome.
Reports of Anomalous Amelogenin Alleles: •Males possessing only a single X amelogenin amplicon (Y null) – a male DNA sample will falsely look like a female DNA sample oSantos et al. (1998) reported a rare deletion of the amelogenin gene on the Y-chromosome oY-STR typing can be performed to verify that other portions of the Y-chromosome are present •Males possessing only a single Y amelogenin amplicon (X null): oShewale et al. 2000) observed loss of the X chromosome amplicon in three out of almost 7,000 males examined owhile this phenomenon should not result in a gender misclassification (as the Y null situation might), its occurrence can impact the expected X and Y amplicon ratios in a mixture (see NIST MIX05 interlab study, case #3) Problems may arise not only from false detection (or non-detection) of amelogenin-specific fragments, but also in cases of chimerism (bone marrow transplants) or micro chimerism (pregnant women carrying male fetuses), and from the possible discrepancies between the biological gender and the forensic relevant) legal gender in the personal identity documents. CONCLUSION: One should keep in mind, that an X- or a Y-chromosome – be it detected with amelogenin or y-specific STR typing – does not necessarily tell the truth about the registered gender and the gender identity Lastly to quote in the words of Eric Vilain: Sex should be easily definable, but it’s not. Our gender identity, our profound sense of being male or female is independent from our anatomy.