DNA Phenotyping 🧬

Shivi Forensics
TOPIC: DNA Phenotyping 

Written By: 
Hrigvi Singh Banafar
Volunteer, Shivi Forensics


INTRODUCTION
DNA contains the instructions for much of our body's development and function. This genetic material acts like a blueprint, dictating everything from our eye color to our hair texture. While DNA is widely recognized for its role in identifying individuals, such as matching a suspect to a crime scene, scientific advancements now allow for a different insight: predicting physical characteristics directly from a DNA sample.

DNA phenotyping predicts an individual's observable physical traits (phenotype) and biogeographical ancestry by analyzing their DNA. This technique goes beyond simply identifying a person through a direct DNA match. Instead, it reconstructs characteristics like eye color, hair color, skin tone, and some facial features from a biological sample. It generates a descriptive profile of an unknown individual, providing insights into their appearance and heritage. During investigations, forensic DNA phenotyping serves as a "biological witness" and may provide more reliable and accurate information regarding the physical description of the contributor in comparison to human eyewitness testimonies, thereby providing potential investigative leads.

BEHIND PHENOTYPIC PREDICTION
DNA phenotyping operates by analyzing specific genetic markers. Scientists examine single nucleotide polymorphisms (SNPs), which are variations at a single point in the DNA sequence. Hundreds of thousands or even millions of these SNPs are tested for their association with particular traits. For instance, certain SNPs are strongly linked to variations in eye or hair color.

These genetic markers are correlated with observable characteristics using advanced statistical models and extensive databases. These models are built from large populations where both DNA and physical traits are known, allowing researchers to determine the probability of certain features appearing with specific genetic variations. Predicting polygenic traits is more complex than predicting monogenic traits. The accuracy of these predictions can vary depending on the trait, with some traits like eye color having higher prediction accuracy than others.

FORENSIC APPLICATIONS
The HIrisPlex-S DNA test system is considered the first forensically validated tool to simultaneously predict eye, hair, and skin color from DNA samples, including samples consisting of degraded DNA and/or low-quantity DNA. The developmental validation was conducted in accordance with the SWGDAM guidelines, including sensitivity, stability, mixtures, and simulated casework-type samples. This test system involves two SNaPshot-based multiple assays analyzing a total of 41 SNPs, which includes a multiplex assay for 17 skin color-predicting SNPs and 24 hair and eye color-predicting SNPs. The IrisPlex-S system is capable of predicting five levels of skin pigmentation: very pale, pale, intermediate, dark, and dark black. It can also conduct predictions for four hair colors: blond, brown, red, and black.

LIMITATIONS OF DNA PHENOTYPING
1. Accuracy issues
Predictions for simple monogenic traits like eye color achieve higher reliability (74-99%), but polygenic traits such as facial shape or height suffer from lower precision due to multiple gene interactions and insufficient reference data. Environmental influences, including diet, aging, or sun exposure, alter phenotypes beyond genetic predictions, leading to mismatches. Dataset quality and population diversity also impact results, with biases reducing effectiveness across ethnic groups.

2. Ethical concerns
Privacy violations arise from analyzing DNA without consent, potentially enabling surveillance or misuse of genetic profiles. Risks include racial profiling from ancestry inferences and discrimination. based on predicted traits. Lack of regulation exacerbates fears of unauthorized phenotyping from public or familial samples.

3. Practical constraints
Degraded or mixed DNA samples hinder reliable marker identification, while high costs and specialized equipment limit accessibility. Predictions provide probabilities, not certainties, requiring corroboration with other evidence to avoid investigative errors.

CONCLUSION
It can be stated that obtaining a set of genetic markers that accurately predict most of human EVCs for forensic use is closer than ever, and a complete "DNA facial composite" is already in sight for forensic routine. Also, despite the many ethical and legal issues that still permeate this subject, the high statistical accuracy of most of these studies makes them viable for practical use in forensic routines.

REFERENCES


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