What is DNA profiling and how does it help solve crimes?

The first step in DNA profiling consists of procuring relevant DNA samples. Only a small number of cells from a person’s skin or the root of a hair or from bodily fluids like blood, saliva, or semen is needed to build a unique DNA profile. Usually DNA samples are taken from crime scenes. If not, people can be asked to give up samples voluntarily. If there is enough info and evidence, someone may be ordered by law to provide DNA samples.

According to the article: "Once forensic scientists obtain a sample, they extract the DNA from cells in bodily fluids or tissues and copy it. They then separate the copied markers using a process known as capillary electrophoresis. This enables them to identify distinct markers and the number of repeats for different markers in each allele. The forensic scientists read this data using a chart called an electropherogram, which plots fragments of DNA and shows how many repeats there are for each marker and where they occur. Based on this chart, forensic scientists generate a DNA profiling definition that law enforcement professionals can read. This definition consists of a simple list of numbers, indicating how many repeat units are in each allele of 20 marker points throughout the person’s genome."

This article gives some examples of cases where this DNA profiling tool has been put into affect. It also talks about the history of DNA profiling as well as some pros and cons. I strongly recommend this article.

Ryan Press explains how DNA profiling is a powerful tool for solving crimes, especially when the DNA evidence involves just one or two individuals. However, with advancements in technology, forensic scientists can now analyze DNA mixtures and trace amounts of DNA, like “touch DNA" ,(skin cells) making interpretation more complex. These new methods allow investigators to handle more sensitive evidence but also introduce uncertainties with these results. As DNA mixtures become more common, understanding these uncertainties is crucial for accurate interpretations in investigations and courtrooms.

The new methods in DNA analysis include advancements in DNA mixture analysis, which helps separate and interpret overlapping profiles from multiple samples at a crime scene. Forensic scientist now use “touch DNA” to detect even small amounts of DNA left behind from simple contact, making it easier to gather evidence from everyday surfaces. (people leaving behind skin cells when touching something) However, this also increases the chances of irrelevant DNA being detected. To manage these mixtures, forensic scientists rely on probabilistic genotyping software (PGS), which uses statistical models to estimate how likely it is that a suspect’s DNA contributed to the evidence. Also, high-sensitivity DNA method, like PCR, amplify small or degraded DNA samples, which help investigators to analyze even the smallest amounts of genetic material. These advancements offer powerful tools for crime scenes but also require careful analysis due to their problems.

Back in 1995, the National Institute of Justice (NIJ) started looking into how DNA could help clear people who were wrongfully convicted. This led to the creation of the National Commission on the Future of DNA Evidence, with the goal of improving how DNA is used in the criminal justice system. The Commission was led by Chief Justice Shirley S. Abrahamson and included members from all parts of the justice system. They focused on crime scene investigations, evidence collection, and the growing use of DNA technology to solve old cases, including those through the Combined DNA Index System (CODIS).

The rise of DNA databases and advancements in DNA technology have completely changed how criminal investigations are done. Initially, these databases were only used for violent crimes, but now they include profiles of all convicted felons, making them much more effective. New legal tactics, like "John Doe" warrants based on DNA profiles, allow authorities to keep cases open until they find a match. Technologies like PCR and STR have made it possible to analyze smaller or even degraded samples from cold cases, and CODIS helps connect crimes across different states by matching DNA profiles.

Y-chromosome analysis is another forensic tool that focuses on male-specific genetic markers, which is particularly helpful in cases where there are multiple male contributors to a biological sample. Since the Y-chromosome is passed from father to son, it can also be used to trace male family relationships. This technique might reduce the need to separate biological cells in evidence like rape kits. However, DNA profiles from Y-chromosome testing don’t work with CODIS, which mainly uses STR analysis for its database. Collaboration with crime labs is essential to figure out the best approach for each case.

I think this article gave some very good and precise example on how DNA can help us investigate crime cases, and delves deep into the details behind getting the tech necessary in order to use DNA in this manor. I strongly encourage reading this article.