DNA contamination
Dear Caz,
Thank you for your welcome.
The 2002 judgment does not seem to be very specific regarding other profiles bar Hanratty's. I understand that you can identify female DNA without going to the trouble of a full test and it may be that it was not felt worthwhile testing DNA which was obviously Valerie's. Similarly Gregsten's DNA may have been surmised from the blood grouping match from 1961. I have not read anything about his body having been exhumed or his family having been approached for samples though again I would not have thought that there was any need. If so it may be that only one male DNA sample was found.
I recall someone quoting a TV documentary wherein one of the scientists (Dr Mann?) was quoted as saying exactly that (that only one male profile was obtained) but he may simply have meant one additional profile to the known contribution from Michael Gregsten. Either way no "strange" profiles were found though this may not be surprising. Whilst I do not have much of an understanding of the details behind the science I did note from a paper on the subject that it is very difficult to identify individual DNA when you have a mix of three or more profiles, particularly where the samples are small. In this case there was an identifiable portion (Hanratty's) as well as a female portion (Valerie's) which may have made matters easier but whether or not other samples would merge to become undetectable I do not know. The paper referred to suggested that the difficulties encountered became worse over time and they were only referring to a few weeks, not forty years. If the exhibits were extracted from the files (and I think that they would have been on several if not many occasions) the resulting exposure to air would have greatly increased the likelihood of degradation of the original DNA. If the glass vial was broken much later than this it would explain why Hanratty's DNA remained whereas other contributions were undetectable.
All in all I think that contamination was probable rather than possible but I appreciate that any such contamination event could simply have added more of Hanratty's DNA to DNA of his that was already there. If so it would be yet another strange co-incidence in this complicated saga.
James
Dear Caz,
Thank you for your welcome.
The 2002 judgment does not seem to be very specific regarding other profiles bar Hanratty's. I understand that you can identify female DNA without going to the trouble of a full test and it may be that it was not felt worthwhile testing DNA which was obviously Valerie's. Similarly Gregsten's DNA may have been surmised from the blood grouping match from 1961. I have not read anything about his body having been exhumed or his family having been approached for samples though again I would not have thought that there was any need. If so it may be that only one male DNA sample was found.
I recall someone quoting a TV documentary wherein one of the scientists (Dr Mann?) was quoted as saying exactly that (that only one male profile was obtained) but he may simply have meant one additional profile to the known contribution from Michael Gregsten. Either way no "strange" profiles were found though this may not be surprising. Whilst I do not have much of an understanding of the details behind the science I did note from a paper on the subject that it is very difficult to identify individual DNA when you have a mix of three or more profiles, particularly where the samples are small. In this case there was an identifiable portion (Hanratty's) as well as a female portion (Valerie's) which may have made matters easier but whether or not other samples would merge to become undetectable I do not know. The paper referred to suggested that the difficulties encountered became worse over time and they were only referring to a few weeks, not forty years. If the exhibits were extracted from the files (and I think that they would have been on several if not many occasions) the resulting exposure to air would have greatly increased the likelihood of degradation of the original DNA. If the glass vial was broken much later than this it would explain why Hanratty's DNA remained whereas other contributions were undetectable.
All in all I think that contamination was probable rather than possible but I appreciate that any such contamination event could simply have added more of Hanratty's DNA to DNA of his that was already there. If so it would be yet another strange co-incidence in this complicated saga.
James
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