24-04-2008, 21:46:41
Morenohijazo,
Sobre las mezclas le remito a mis posts #5233 y #5258
Destaco el extracto del manual de INTERPOL sobre el intercambio y la utilización de datos relativos a ADN:
"No obstante, se plantean
problemas cuando se analizan muestras forenses que consisten en una
mezcla de fluidos corporales, ya que en este caso el perfil del ADN es
demasiado complejo para que se pueda interpretar"
"Interpol propone que se establezca una base de datos internacional de
perfiles de ADN identificados y no identificados (es decir, procedentes
de muestras obtenidas en el lugar del delito y de muestras de
referencia) para uso de sus Estados Miembros. Los países podrán
incorporar perfiles de sus bases de datos nacionales o regionales y
compararlos con los suministrados por los Estados Miembros de
Interpol participantes. (...) [b] Los perfiles obtenidos de
muestras mezcladas no se almacenarán en la base de datos[/]"
Si lo dicen ellos, será por algo, no?
Y por si le queda alguna duda de que la interpretación de las mezclas de perfiles es un asunto problemático, vea este editorial:
Forensic Science International 160 (2006) 89
Editorial on the recommendations of the DNA commission of
the ISFG on the interpretation of mixtures
The rapid evolution of forensic DNA analysis based on
typing results from short tandem repeat (STR) polymorphisms
has dramatically increased the significance of biological stains
in criminal court proceedings. It has come to the point where
DNA evidence alone could be decisive for obtaining a
conviction of an accused suspect. Thus the interpretation of
the observed DNA profile of a given stain in the context of the
case needs to include a reasonable biostatistical evaluation of
the weight of the evidence. At the same time, the molecular
biological tools available to the forensic geneticist have become
more and more sensitive to the point where the genomic DNA
from a few dozen cells may be sufficient to obtain a full STR
profile from an unknown offender. As a result, the number of
DNA mixtures composed from full or partial profiles from two
or more contributors (who could be offenders, victims, or
individuals not associated with the crime event) has increased
significantly. The biostatistical interpretation of such mixed
DNA profiles is a very challenging task that sometimes leads to
controversial views about correct mathematical approaches for
estimating the weight of the evidence. Indeed, diverse practices
have already arisen between laboratories, hence there is an
urgent need to formulate recommendations.
As the main peer review body of the forensic community
dealing with DNA profiling, the International Society of
Forensic Genetics (ISFG) has already published numerous
recommendations on issues related to nomenclature validation,
and interpretation of autosomal, Y-chromosome and mitochondrial
DNA typing systems. Typically, the DNA Commission
will evaluate an area where sufficient, albeit sometimes
uncoordinated scientific evidence, has been established from
original research studies. This accumulated experience is used
to formulate recommendations to serve as guidelines to
standardize the use of new typing systems—a crucial
prerequisite in forensic casework. In the recommendations of
the ISFG Commission on mixture interpretation (Gill et al.,
2006), the Commission has gone beyond this basic task. These
recommendations have been written to serve two purposes: to
define a generally acceptable mathematical approach for
typical mixture scenarios and to address open questions where
practical and generally accepted solutions do not yet exist. This
has been done to stimulate the discussion among scientists in
this field. The aim is to invite proposals and criticism in the
form of comments and letters to the editors of this journal, as
well as by opening a discussion forum on the website of the
society (http://www.isfg.org, available when the manuscript
appears in print).
This paper is a ‘high level’ treatise on the mathematical
principles to analyse complex mixtures. We realise that it will
not be possible for most laboratories to immediately implement
the methods described. Our intention is primarily to specify a
consensus approach to act as the foundation stone. Hopefully
we will encourage the development of expert systems to take
care of the onerous calculations.
However, we also intend to describe pragmatic approaches
to interpret mixtures. By comparing results against the
mathematical principles described in this paper, the intention
is to ensure that pragmatic approaches do not act in a nonconservative
way. Often there are limitations to approaches, and
our purpose will be to highlight these.
We are hoping to continue the process to allow the DNA
Commission to critically revise or extend these recommendations
in due time (hopefully at the next ISFG congress in
Copenhagen in 2007).We are aware that the DNA Commission
has not been able to offer solutions for the entire range of
challenging samples that we encounter in our daily casework,
but we hope having made a first step in the right direction by
publishing the present recommendations.
Peter M. Schneider
Peter Gill
Angel Carracedo
------------------------
Qué idiotez más grande sería todo esto, tanto análisis estadístico y tanta carallada, de ser cierto que repartiendo los alelos de una mezcla entre los perfiles conocidos ya queda el asunto resuelto.
Sobre las mezclas le remito a mis posts #5233 y #5258
Destaco el extracto del manual de INTERPOL sobre el intercambio y la utilización de datos relativos a ADN:
"No obstante, se plantean
problemas cuando se analizan muestras forenses que consisten en una
mezcla de fluidos corporales, ya que en este caso el perfil del ADN es
demasiado complejo para que se pueda interpretar"
"Interpol propone que se establezca una base de datos internacional de
perfiles de ADN identificados y no identificados (es decir, procedentes
de muestras obtenidas en el lugar del delito y de muestras de
referencia) para uso de sus Estados Miembros. Los países podrán
incorporar perfiles de sus bases de datos nacionales o regionales y
compararlos con los suministrados por los Estados Miembros de
Interpol participantes. (...) [b] Los perfiles obtenidos de
muestras mezcladas no se almacenarán en la base de datos[/]"
Si lo dicen ellos, será por algo, no?
Y por si le queda alguna duda de que la interpretación de las mezclas de perfiles es un asunto problemático, vea este editorial:
Forensic Science International 160 (2006) 89
Editorial on the recommendations of the DNA commission of
the ISFG on the interpretation of mixtures
The rapid evolution of forensic DNA analysis based on
typing results from short tandem repeat (STR) polymorphisms
has dramatically increased the significance of biological stains
in criminal court proceedings. It has come to the point where
DNA evidence alone could be decisive for obtaining a
conviction of an accused suspect. Thus the interpretation of
the observed DNA profile of a given stain in the context of the
case needs to include a reasonable biostatistical evaluation of
the weight of the evidence. At the same time, the molecular
biological tools available to the forensic geneticist have become
more and more sensitive to the point where the genomic DNA
from a few dozen cells may be sufficient to obtain a full STR
profile from an unknown offender. As a result, the number of
DNA mixtures composed from full or partial profiles from two
or more contributors (who could be offenders, victims, or
individuals not associated with the crime event) has increased
significantly. The biostatistical interpretation of such mixed
DNA profiles is a very challenging task that sometimes leads to
controversial views about correct mathematical approaches for
estimating the weight of the evidence. Indeed, diverse practices
have already arisen between laboratories, hence there is an
urgent need to formulate recommendations.
As the main peer review body of the forensic community
dealing with DNA profiling, the International Society of
Forensic Genetics (ISFG) has already published numerous
recommendations on issues related to nomenclature validation,
and interpretation of autosomal, Y-chromosome and mitochondrial
DNA typing systems. Typically, the DNA Commission
will evaluate an area where sufficient, albeit sometimes
uncoordinated scientific evidence, has been established from
original research studies. This accumulated experience is used
to formulate recommendations to serve as guidelines to
standardize the use of new typing systems—a crucial
prerequisite in forensic casework. In the recommendations of
the ISFG Commission on mixture interpretation (Gill et al.,
2006), the Commission has gone beyond this basic task. These
recommendations have been written to serve two purposes: to
define a generally acceptable mathematical approach for
typical mixture scenarios and to address open questions where
practical and generally accepted solutions do not yet exist. This
has been done to stimulate the discussion among scientists in
this field. The aim is to invite proposals and criticism in the
form of comments and letters to the editors of this journal, as
well as by opening a discussion forum on the website of the
society (http://www.isfg.org, available when the manuscript
appears in print).
This paper is a ‘high level’ treatise on the mathematical
principles to analyse complex mixtures. We realise that it will
not be possible for most laboratories to immediately implement
the methods described. Our intention is primarily to specify a
consensus approach to act as the foundation stone. Hopefully
we will encourage the development of expert systems to take
care of the onerous calculations.
However, we also intend to describe pragmatic approaches
to interpret mixtures. By comparing results against the
mathematical principles described in this paper, the intention
is to ensure that pragmatic approaches do not act in a nonconservative
way. Often there are limitations to approaches, and
our purpose will be to highlight these.
We are hoping to continue the process to allow the DNA
Commission to critically revise or extend these recommendations
in due time (hopefully at the next ISFG congress in
Copenhagen in 2007).We are aware that the DNA Commission
has not been able to offer solutions for the entire range of
challenging samples that we encounter in our daily casework,
but we hope having made a first step in the right direction by
publishing the present recommendations.
Peter M. Schneider
Peter Gill
Angel Carracedo
------------------------
Qué idiotez más grande sería todo esto, tanto análisis estadístico y tanta carallada, de ser cierto que repartiendo los alelos de una mezcla entre los perfiles conocidos ya queda el asunto resuelto.