Forensic DNA Phenotyping

BY SIFS India | November 16, 2022

Forensic DNA Phenotyping | Predicting Human Appearances

DNA phenotyping is a technique in which the physical appearance (phenotype) of a person is predicted from the source of DNA (DNA sample).

Genetics of Appearance

There are different genes ( more specifically SNP markers) that are regulating the phenotypes of an individual.

The physical traits of an individual are complex as they are controlled by many genes. In other words, they are product of complex inheritance between different genes.

Also, there is an influence of environmental factors on these traits and thus they vary continuously. Environmental factors include pollution or toxic substances in the environmental nutrition of an individual etc.

Forensically this technique is useful as:

1. To identify a missing person on the basis of a DNA sample acquired from the scene of the crime. ( for example:- from skeletal remains, unknown mutilated dead bodies etc)

2. To narrow down the list of suspected people on the basis of DNA samples obtained from the crime scene.

How Does Forensic DNA Phenotyping Work?

This technique takes advantage of modern SNP technology.

DNA is a blueprint of an individual. It defines our hair colour, eye colour, skin colour and all other traits. All this information is stored in the DNA in the form of codes.

This technique uses GWAS (Genome-Wide Association Study) approach in which genetic variants (mostly SNP markers) that are associated with the target trait are discovered. After that with the use of predictive modeling, predictions of the traits are made.

For prediction, there are 2 methods:

Direct Method: In this, statistical methods are used and information is gathered about the trait value. Also, genetic variants are linked mechanically with the relevant phenotypic expression.

Indirect Method: In this, variants that are associated with genetic components of ancestors are used to gather information about trait value. These are then combined with appropriate statistical methods.

Table no. 1 - FDP Vs DNA Profiling

FDP	DNA
In FDP known sample is not required.	For DNA analysis, identification of a person is done through STR profile matching of an evidence (i.e. DNA sample) obtained from a scene of the crime along with a reference sample from a known person.
FDP only focuses on SNP (Single Nucleotide Polymorphism) markers and DNA loci that are responsible for physical traits.	In DNA analysis each loci in number of tandem repeats of DNA base pairs is focused and analyzed that are responsible for variation.

Limitations of FDP Technique

- It is not completely developed in the field of forensic biology. For this reason it has not been implemented within this field.

- It may not be accurate in case of artificially altered appearances and may give unpredicted results.

- More and accurate markers have to be known for more accurate results.

Due to all the above limitations, results of this technique are used as supportive evidence and not a main evidence in a court of law.

Traits That Can be Known Through FDP

FDP predicts the Externally Visible Characteristics (EVC’S) of an individual. By using this technique, gender, hair color, iris colour, and skin color of a person can be known.

Future Advances in This Technique

Future FDP developments can be made in detection of physical traits like:

- Body height

- Baldness

- Age

- Hair structure

- Face