Forensic Genealogy, Phenotype Identification, and Other Trends in Forensic Genetics
As a Biology major with a Master’s degree in Forensic Genetics, I might be biased when I say that genetics is one of the most fascinating scientific fields. These individual lines of code predetermine who we are, how we look, and sometimes how we behave. I’ve studied the influence of DNA mutations on blood disease symptoms, tried to determine if microbial metabolites could help estimate the time of death, and even began exploring the different facets of forensic virology.
The potential of DNA analysis in a forensic context is never-ending. New discoveries lead to new ideas, new technologies, and new methodologies. And that’s more than enough to keep me in love with this field.
DNA analysis has irreversibly changed how the criminal justice system works. Since the introduction of genetics to the forensic sciences, millions have been proven guilty or found innocent while facing criminal accusations.
Forensic genetics uses knowledge regarding DNA-specific properties and applies it to solving crimes, identifying missing individuals and remains, and confirming familial relationships between different people.
This field is rapidly expanding as researchers try to find new solutions to newfound problems. Recent advancements include forensic genetic genealogy, forensic microbiology, and phenotype identification.
In this article, we’ll be going over these topics as well as other interesting and relevant advances in the field of forensic genetics.
Forensic Genealogy, Phenotype Identification, and Other Trends in Forensic Genetics
The forensic genetics field improved greatly as new DNA discoveries were made throughout the years. Every day, new technology and methodology are developed, making the practices a lot faster, cheaper, and accessible.
New problems also require unique solutions, and researchers keep their hands full while coming up with new ways to evolve in this field. Let’s take a look at some of the most recent developments in forensic genetics.
DNA Analysis Using Massively Parallel Sequencing (Next-Generation Sequencing)
Massively parallel sequencing (MPS) or next-generation sequencing (NGS) techniques can generate millions of sequencing reads in a single run. They can be used, for example, to quickly sequence an entire genome.
In forensic genetics, these techniques are used to target different DNA markers in one assay, increasing the discrimination power of the analysis. MPS is also successful when working with challenging, low-level, and degraded DNA samples.
MPS’ precision allows the discrimination of small DNA variations that would easily be undetected using capillary electrophoresis, the most common sequencing technique.
DNA Mixture Interpretation
DNA mixtures include several sources of DNA that need to be distinguished to obtain the genomic profiles of everyone who contributed to it. It can prove quite a complicated task due to the number of alleles that need to be differentiated and the often low quality of the samples.
Mixtures are mostly recovered from scenarios involving some sort of sexual offense. However, DNA mixtures can also originate from items that have been handled by several individuals, for example.
Recent, sensitive STR profiling techniques allow better recovery of mixed DNA profiles. Instead of simply determining if an individual can be excluded as a contributor to the mixture, these techniques can estimate the most likely genotype combinations of potential contributors.
Identifying Body Fluids Through RNA Profiling
Knowing what kind of fluids are present at a crime scene, in a timely manner, can help guide the investigation and provide different ideas regarding what went on during the incident. Even more so when a DNA profile is then linked to that biological sample.
Using DNA to identify body fluids has some limitations including the lack of sensitivity, low specificity, and destruction of limited DNA samples. Therefore, RNA was always preferred for these investigations.
RNA can be co-extracted alongside DNA. This means that a DNA profile can be created at the same time as the body fluid is identified. At the same time, RNA is tissue-specific which quickly helps the identification of specific body fluids.
Recently, studies regarding body fluid identification have been focusing on micro RNAs (miRNAs) instead of messenger RNAs (mRNAs). miRNAs are tissue-specific like mRNAs but are much smaller and more stable in comparison.
Different assays that use panels of different miRNAs are now used to identify specific body fluids. miRNAs are also of interest in forensic genetics as they can be used to estimate the time of depositions of fluid stains and the post-mortem interval.
Forensic DNA Phenotyping
A phenotype is a set of observable characteristics of an individual that result from the interaction between their genotype and the environment. Eye, hair, and skin color are a few examples of some of these observable characteristics.
It is possible to use DNA analysis to predict externally visible characteristics (EVCs). This has led to the development of assays that use DNA samples recovered from crime scenes to predict how a potential suspect might look.
Knowing that they might have a certain skin or eye color can help narrow down the search pool and lead the investigation in a more focused direction. These techniques are also helpful in missing person cases and disaster victim investigations.
The most successful assays are used to predict human pigmentation traits however, DNA phenotyping isn’t just limited to the prediction of EVCs. It can also be used to infer bio-geographic ancestry and estimate age using epigenetic markers.
There are already a few forensically validated tests available, namely the IrisPlex, HIrisPlex, and HirisPlex-S. Unfortunately, this technology is not allowed in several countries. Complex legal and ethical issues surrounding EVC prediction still need to be resolved.
Epigenetics and DNA Methylation Analysis
Particular behaviors and the environment can modify how certain genes work through mechanisms like DNA methylation. These modifications are called epigenetic changes. They are contained inside the DNA molecule and can also be used for forensic purposes.
DNA methylation plays an important role in cell differentiation and appears at different rates in different tissues. This way, epigenetic markers can be used to identify the tissue sources of different body fluids found at crime scenes.
DNA methylation analysis can also be used to estimate the age of individuals through their DNA samples, discriminate monozygotic twins, and determine a suspect’s smoking habits.
Forensic Genealogy
Companies like 23andMe, AncestryDNA, and FamilyTreeDNA made DNA testing extremely popular. People resort to their services to discover more about their ancestry and also receive health insights according to their genes.
The results of these tests are compiled in huge public databases like GEDmatch. They allow people who take the tests to identify potential relatives, conducting their own genealogical research.
These databases have also proven helpful in solving criminal investigations. In fact, using genetic genealogy in a forensic context permitted the high-profile arrest of the Golden State Killer, Joseph DeAngelo, in 2018.
When investigators have a DNA sample from a suspect that they can’t match, they can access these databases and look for relatives of the potential perpetrator. Once they have a familial match, they can narrow down their search to members of that specific family, until they find the suspect.
Microbial DNA Analysis
According to the Human Microbiome Project (HMP), there are ten times more microbes in the human body than there are human cells. The human microbiome is highly specific to individuals and particular microbial communities colonize different organs of the body. Even people who inhabit the same space have their own microbial signature.
Given these properties, it’s not hard to determine how microbial DNA analysis can be helpful in forensic investigations. In fact, the US National Institute of Justice is currently focusing its efforts on a few forensic applications of microbiomes.
They study the necrobiome to help determine the time of death of individuals. They can also study the microbiome found in different soils to potentially match it with a victim, suspect, or evidence. And finally, they also use the trace human microbiome to link a victim or suspect to certain objects or environments.
Forensic Genealogy, Phenotype Identification, and Other Trends in Forensic Genetics — Final Considerations
The discovery of DNA and its properties revolutionized investigations in criminal justice cases. It sometimes might seem that DNA analysis in forensic contexts is solely used to identify suspects. However, that idea couldn’t be further from the truth.
As research progresses, new technologies and methodologies appear, each of them with new potential when it comes to aiding criminal investigations.
Current trends in forensic genetics include massively parallel sequencing, new DNA mixture interpretation methods, body fluid identification through miRNA, and forensic phenotyping. DNA methylation patterns, forensic genealogy, and microbial DNA analysis are also recent innovations used in criminal investigations.
Some of these practices need to be further optimized and regulated to become the norm. However, with caution and care, the potential benefits of each methodology in forensic practice can expand.
References:
Niamh Nic Daeid, Lucina Hackman, Penelope R. Haddrill; Developments in forensic DNA analysis. Emerg Top Life Sci 24 September 2021; 5 (3): 381–393.
Kevin Wai Yin Chong, Zhonghui Thong, Christopher Kiu‐Choong Syn; Recent trends and developments in forensic DNA extraction. WIREs Forensic Sci. 2021; 3:e1395.
Elvira Ventura Spagnolo, Chiara Stassi, Cristina Mondello, Stefania Zerbo, Livio Milone, Antonina Argo; Forensic microbiology applications: A systematic review. Legal Medicine. 2019; 36: 73–80.
Jake M. Robinson, Zohar Pasternak, Christopher E. Mason, Eran Elhaik; Forensic Applications of Microbiomics: A Review. Frontiers in Microbiology. 2021; 11:608101.
