Genotype (DNA) → Biological pathways → Physical traits (Phenotype)

• Traditional forensics = Who is this?
• FDP = What might this person look like?

Genetic Basis (Deep Science)

A. SNPs (Single Nucleotide Polymorphisms)

• FDP mainly relies on SNP markers, not STRs
• SNP = variation at a single base (A, T, G, C)
• Example: A → G change affecting pigmentation

 Why SNPs?

• More stable than STRs
• Better for degraded DNA
• Directly linked to functional traits

B. Pigmentation Genetics

Key Genes:

• OCA2 & HERC2 → Eye color (blue/brown variation)
• MC1R → Red hair phenotype
• SLC24A5, SLC45A2 → Skin pigmentation
• TYR (Tyrosinase) → Melanin production

Mechanism:

• Melanin types:
  • Eumelanin → Brown/black
  • Pheomelanin → Red/yellow

 Variation in these genes alters melanin production → visible traits

C. Polygenic Nature of Traits

• Most traits are polygenic (controlled by many genes)
• FDP uses statistical models combining multiple SNPs

Example:

• Eye color prediction may use ~6–20 SNPs
• Skin color may use >30 SNPs

3. Laboratory Workflow (Technical Pipeline)

 Step 1: DNA Extraction

• Methods: Organic extraction, Chelex, silica-based
• Works even on:
  • Degraded samples
  • Trace DNA

Step 2: DNA Quantification

• Using qPCR (Quantitative PCR)
• Ensures enough DNA for sequencing

Step 3: Library Preparation

• DNA fragmented + adapters added
• Target SNP regions amplified

Step 4: Sequencing (NGS)

• Platforms:
  • Illumina MiSeq
  • Ion Torrent

 Generates millions of reads covering SNP regions

Step 5: Bioinformatics Analysis

• Raw data → cleaned → aligned to reference genome
• SNP calling performed
• Output: genotype (AA, AG, GG)

Step 6: Prediction Modeling

• Algorithms used:
  • Logistic regression
  • Bayesian models
  • Machine learning

Step 7: Facial Approximation

• Software converts predictions into:
  • 2D sketches
  • 3D models

Prediction Systems

 HIrisPlex System

• Predicts eye & hair color
• Accuracy:
  • Eye color: ~90%
  • Hair color: ~70–80%

 HIrisPlex-S

• Adds skin color prediction

 SNAPSHOT (Parabon NanoLabs)

• Generates facial composites

Accuracy & Reliability