Tag Archives: DNA

University of Melbourne and Aalborg University study: How convincing is a Y-chromosome profile match between suspect and crime scene? Study aims to improve the validity and intelligibility of Y-chromosome evidence presented in court

4 Nov

Sarah C. P. Williams wrote in the Science article, Y Chromosome Is More Than a Sex Switch:

The small, stumpy Y chromosome—possessed by male mammals but not females, and often shrugged off as doing little more than determining the sex of a developing fetus—may impact human biology in a big way. Two independent studies have concluded that the sex chromosome, which shrank millions of years ago, retains the handful of genes that it does not by chance, but because they are key to our survival. The findings may also explain differences in disease susceptibility between men and women.
“The old textbook description says that once maleness is determined by a few Y chromosome genes and you have gonads, all other sex differences stem from there,” says geneticist Andrew Clark of Cornell University, who was not involved in either study. “These papers open up the door to a much richer and more complex way to think about the Y chromosome….” http://www.sciencemag.org/news/2014/04/y-chromosome-more-sex-switch

See, National Institute of Standards and Technology study: Courtroom use of ‘Likelihood Ratio’ not consistently supported by scientific reasoning approach https://wordpress.com/posts/drwilda.com and More Innocent People on Death Row Than Estimated: Study http://time.com/79572/more-innocent-people-on-death-row-than-estimated-study/

Science Daily reported in How convincing is a Y-chromosome profile match between suspect and crime scene?

David Balding of the University of Melbourne, Australia and Mikkel Andersen of Aalborg University in Denmark have developed new, open-source software that can help understand how many people in a population will match a single Y-chromosome profile detected at a crime scene, which they describe in a new study in PLOS Genetics.
Forensic analysis of Y-chromosome DNA is especially useful when a small amount of male DNA is mixed in with a large amount of female DNA, such as occurs in sexual assault cases. Explaining this evidence in court, however, is difficult because the Y chromosome passes down mostly unchanged from fathers to sons, so a single Y-chromosome profile can be shared by dozens of men in a population.
Instead of a match probability or database count, Balding and Andersen propose that courts be told about the likely number of matching males in the population, and the possible consequences of their relatedness, which is often more distant than uncle or cousin but much closer than for a random man. They also show how the distribution of matching males can be affected by database information, and suggest ways to present this information in court to make clear that Y-chromosome evidence cannot definitively identify the culprit, but can dramatically reduce the number of possible sources of the DNA. The court must then decide if it has enough other evidence to identify the suspect as the source of the Y-chromosome profile, rather than one of his matching (distant) relatives.
After the introduction of DNA profiling using non-sex chromosomes, the procedure had problems that, once addressed, made profiling a powerful tool that has revolutionized forensic science. Now, Y chromosome profiling must undergo the same process to quantify the results in a way that is valid and directly interpretable to courts. The new software presented in this study could be used to improve the accuracy of Y chromosome evidence and to increase its understanding by judges and jurors…. https://www.sciencedaily.com/releases/2017/11/171103142725.htm

Citation:

How convincing is a Y-chromosome profile match between suspect and crime scene?
Study aims to improve the validity and intelligibility of Y-chromosome evidence presented in court
Date: November 3, 2017
Source: PLOS
Summary:
Scientists have developed new, open-source software that can help understand how many people in a population will match a single Y-chromosome profile detected at a crime scene.
Journal Reference:
1. Mikkel M. Andersen, David J. Balding. How convincing is a matching Y-chromosome profile? PLOS Genetics, 2017; 13 (11): e1007028 DOI: 10.1371/journal.pgen.1007028

Here is the press release:

Public Release: 3-Nov-2017
How convincing is a Y-chromosome profile match between suspect and crime scene?
Study aims to improve the validity and intelligibility of Y-chromosome evidence presented in court
PLOS
David Balding of the University of Melbourne, Australia and Mikkel Andersen of Aalborg University in Denmark have developed new, open-source software that can help understand how many people in a population will match a single Y-chromosome profile detected at a crime scene, which they describe in a new study in PLOS Genetics.
Forensic analysis of Y-chromosome DNA is especially useful when a small amount of male DNA is mixed in with a large amount of female DNA, such as occurs in sexual assault cases. Explaining this evidence in court, however, is difficult because the Y chromosome passes down mostly unchanged from fathers to sons, so a single Y-chromosome profile can be shared by dozens of men in a population.
Instead of a match probability or database count, Balding and Andersen propose that courts be told about the likely number of matching males in the population, and the possible consequences of their relatedness, which is often more distant than uncle or cousin but much closer than for a random man. They also show how the distribution of matching males can be affected by database information, and suggest ways to present this information in court to make clear that Y-chromosome evidence cannot definitively identify the culprit, but can dramatically reduce the number of possible sources of the DNA. The court must then decide if it has enough other evidence to identify the suspect as the source of the Y-chromosome profile, rather than one of his matching (distant) relatives.
After the introduction of DNA profiling using non-sex chromosomes, the procedure had problems that, once addressed, made profiling a powerful tool that has revolutionized forensic science. Now, Y chromosome profiling must undergo the same process to quantify the results in a way that is valid and directly interpretable to courts. The new software presented in this study could be used to improve the accuracy of Y chromosome evidence and to increase its understanding by judges and jurors.
David Balding adds: “We think this work is going to make a big improvement to how Y profile evidence is presented in courts. We will soon extend this work to mixtures of Y-chromosome profiles from multiple males, and also address the corresponding problem for the maternally-inherited mtDNA profiles. Our approach also allows us to include information from any relatives of the suspect whose profile is already available, and we will be working to develop that aspect.”
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In your coverage please use this URL to provide access to the freely available article in PLOS Genetics:
http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1007028
Citation: Andersen MM, Balding DJ (2017) How convincing is a matching Y-chromosome profile? PLoS Genet 13(11): e1007028. https://doi.org/10.1371/journal.pgen.1007028
Image Credit: Mikkel Andersen
Image Caption: A simplified illustration of a simulated population of males, with lines indicating father-son links. The suspected source of the DNA, whose profile matches that from the crime scene, is shown in red and other males with matching Y profiles, who are often close relatives, are yellow. The dashed line separates the last three generations, those further back in time will typically be already dead or otherwise unlikely to be of interest (depending on the circumstances of the crime).
Funding: The authors wish to thank the Isaac Newton Institute for Mathematical Sciences, Cambridge UK, for support and hospitality during the programme Probability and Statistics in Forensic Science, where this paper was conceived. The programme was supported by EPSRC grant no EP/K032208/1. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system. https://www.eurekalert.org/pub_releases/2017-11/p-hci103117.php

Mathew Shaer wrote in the The False Promise of DNA Testing: The forensic technique is becoming ever more common—and ever less reliable.:

Modern forensic science is in the midst of a great reckoning. Since a series of high-profile legal challenges in the 1990s increased scrutiny of forensic evidence, a range of long-standing crime-lab methods have been deflated or outright debunked. Bite-mark analysis—a kind of dental fingerprinting that dates back to the Salem witch trials—is now widely considered unreliable; the “uniqueness and reproducibility” of ballistics testing has been called into question by the National Research Council. In 2004, the FBI was forced to issue an apology after it incorrectly connected an Oregon attorney named Brandon Mayfield to that spring’s train bombings in Madrid, on the basis of a “100 percent” match to partial fingerprints found on plastic bags containing detonator devices. Last year, the bureau admitted that it had reviewed testimony by its microscopic-hair-comparison analysts and found errors in at least 90 percent of the cases. A thorough investigation is now under way…. https://www.theatlantic.com/magazine/archive/2016/06/a-reasonable-doubt/480747/

The reliability of the evidence and the ability of a particular accused to defend against evidence presented in a court hearing is crucial to preventing the innocent from being convicted.

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