What is DNA Phenotyping?

DNA phenotyping is one of many techniques used by forensic scientists. Like other DNA analysis methods, phenotyping is founded on the idea that all humans are genetically unique, with the exception of identical twins. DNA phenotyping uses genetic data to predict the physical appearance of an individual. The advanced technique has multiple applications, from generating criminal leads based on DNA samples found at a crime scene to identifying unknown human remains and solving missing persons cases.

With the right tools and expertise, small DNA samples can be used to generate accurate information on facial features, as well as other traits such as hair, eye and skin colour. It's a complex and fascinating field, which we explore in more detail below.

DNA: 101

Deoxyribonucleic acid, more commonly referred to as DNA, is the bread and butter of almost all living organisms. The organic molecule is found inside cells and carried important genetic information needed for the organism to grow, develop and function.

Information is stored in the form of a code made up of four chemical bases:

• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Thymine (T)

Human DNA is incredibly complex and features around 3 billion bases. The order of these bases determines what information the organism uses to grow, develop and function. It’s these different combinations that make every human genetically unique.

DNA phenotyping in forensic labs

Predicting facial features is one of the most useful applications for DNA phenotyping in forensic labs. Thanks to technological advances like the HIrisPlex-S System, genetic samples can be used to analyse pigmentation data and predict skin, eye and hair colours. DNA phenotyping can also be used to trace biogeographic ancestry and estimate age.

DNA phenotyping is an invaluable technique used by forensic scientists. However, it does have its limits. Unlike forensic short tandem repeat (STR) polymorphism profiling, it can’t be used to identify individuals. For this reason, data is considered an investigative tool, as opposed to clear-cut evidence that can be presented in court. 

“The goal of forensic DNA phenotyping is to narrow down the number of potential crime scene trace donors in such cases to a smaller group of persons who most likely have the externally visible characteristics and biogeographic ancestry that were inferred from the crime-scene DNA,” reads report published in the German science journal Deutsches Arzteblatt International.

The legal and ethical challenges of DNA phenotyping

In the same report, the authors explore the legal and ethical challenges of DNA phenotyping. They stress that while DNA phenotyping is a highly useful tool, the right steps must be taken to minimise privacy violation and ethnic discrimination. They say that to maximise accuracy, avoid discrimination and comply with legal frameworks, forensic scientists combine the three main DNA phenotyping techniques.

“It is therefore strongly recommended that all three techniques of forensic DNA phenotyping, i.e., the prediction of externally visible characteristics, biogeographic ancestry and the estimation of age from DNA should be used together in forensic practice, within an appropriate legal regulatory framework,” reads the article.

Find out more about DNA phenotyping, as well as other forensic techniques such as biosensor fingerprint analysis, palynology and DNA sequencing, in ‘8 Advances in Forensic Science’. Or find out how the specific advancement of automation can make analyses more efficient in the article 'Amino Acid Analysis using Andrew+ Automated Preparation'