Unit 1: Dermatoglyphics - Subjective Questions

Dermatoglyphics is the scientific study of the epidermal ridge patterns present on the fingers, palms, toes, and soles. The term is derived from the Greek words derma (skin) and glyphe (carving).

Significance in Forensic Science:

• Individuality: No two individuals, not even identical twins, share the same fingerprint patterns, making them unique identifiers.
• Permanence: Ridge patterns form during fetal development (around the 10th–16th week of gestation) and remain unchanged throughout life, except in size.
• Personal Identification: Used to establish or confirm the identity of criminals, victims, and unknown persons.
• Crime Scene Investigation: Latent prints recovered from crime scenes can link a suspect to a location or object.
• Legal Admissibility: Fingerprint evidence is widely accepted in courts as a reliable form of identification.

Dermatoglyphics thus forms the foundation of personal identification systems used worldwide.

Recording Rolled Impressions:

• The finger is inked from one edge of the nail to the other.
• Each finger is rolled from nail edge to nail edge on the fingerprint card to capture the entire ridge detail including the sides (deltas).
• Rolling is done in a single, controlled motion to avoid smudging.

Recording Plain (Slap) Impressions:

• The four fingers of each hand are pressed down simultaneously without rolling.
• The thumbs are printed separately.
• Plain impressions are used to verify the sequence and correct placement of the rolled impressions.

Distinction:

Both are recorded on a standard ten-print card for classification and reference.

Henry's Classification System, developed by Sir Edward Henry (with contributions from Azizul Haque and Hem Chandra Bose), is a method for systematically classifying and filing fingerprints based on their patterns.

Key Components:

• The ten fingers are numbered 1–10.
• Whorls are given numerical values based on their position:
  • Fingers 1 & 2: value 16
  • Fingers 3 & 4: value 8
  • Fingers 5 & 6: value 4
  • Fingers 7 & 8: value 2
  • Fingers 9 & 10: value 1
• Only whorls are counted; arches and loops score zero.

Primary Classification Formula:

Importance:

• Enables systematic filing of millions of fingerprint records.
• Allows quick retrieval and comparison.
• Forms the basis of modern AFIS (Automated Fingerprint Identification Systems).

Given whorls on fingers: 2, 3, 6, and 9.

Step 1 — Assign values based on finger position:

• Finger 2 → value 16 (even)
• Finger 3 → value 8 (odd)
• Finger 6 → value 4 (even)
• Finger 9 → value 1 (odd)

Step 2 — Sum even-numbered fingers (numerator):

Step 3 — Sum odd-numbered fingers (denominator):

Step 4 — Apply the primary classification formula:

Primary Classification = 21/10

The constant 1 is added to both numerator and denominator to avoid a value of zero and to ensure a workable fraction.

The three fundamental fingerprint patterns are Arches, Loops, and Whorls.

1. Arches (approx. 5% of patterns):

• Ridges enter from one side and exit the other, rising in the center.
• Plain Arch: Smooth wave-like rise.
• Tented Arch: Sharp upthrust or angle in the center.
• Arches have no delta and no core.

2. Loops (approx. 60–65% of patterns):

• Ridges enter and exit from the same side.
• Contain one delta and one core.
• Ulnar Loop: Opens toward the little finger (ulna).
• Radial Loop: Opens toward the thumb (radius).

3. Whorls (approx. 30–35% of patterns):

• Contain two or more deltas.
• Plain Whorl: Concentric circles with two deltas.
• Central Pocket Loop Whorl: Loop with a small whorl at the center.
• Double Loop Whorl: Two separate loop formations.
• Accidental Whorl: Combination of two or more patterns.

Ulnar Loop vs. Radial Loop:

Key point: The classification depends on the hand, not the direction on paper. A loop that opens toward the little finger of the right hand points in the opposite paper-direction to one on the left hand.

Importance of the Distinction:

• Sub-classification: Helps in the secondary and sub-secondary classification of fingerprints.
• Individualization: Adds precision when narrowing down records.
• Accuracy in comparison: Prevents misclassification during identification, especially in ten-print card filing.

Core:

• The core is the approximate center of a fingerprint pattern.
• In a loop, it is the innermost recurving ridge or the rod rising within it.
• It serves as one of the focal points for ridge counting.

Delta:

• The delta is the point on the first bifurcation, abrupt ridge ending, or divergence of two ridges that surrounds the pattern area, resembling the Greek letter Δ.
• It is the second focal point of a pattern.

Role in Ridge Counting (Loops):

• An imaginary line is drawn from the delta to the core.
• The number of ridges that touch or cross this line (excluding the delta and core themselves) gives the ridge count.

Role in Ridge Tracing (Whorls):

• The ridge emanating from the left delta is traced to the point nearest the right delta.
• The result is classified as Inner (I), Meeting (M), or Outer (O) based on the number of ridges between the tracing ridge and the right delta.

These focal points are essential for precise classification and comparison.

Latent Fingerprints:

• Latent prints are invisible or barely visible impressions left on surfaces by the natural secretions of the skin.
• The word 'latent' means hidden; they require development techniques to be visualized.
• Distinguished from patent prints (visible, e.g., in blood or ink) and plastic prints (three-dimensional impressions in soft materials like wax or clay).

Composition of Fingerprint Residue:

1. Eccrine gland secretions (mostly water ~98%):

• Amino acids
• Sodium chloride and other salts
• Urea, lactic acid
• Glucose, proteins

2. Sebaceous gland secretions (oily):

• Fatty acids
• Glycerides
• Squalene
• Wax esters

3. Apocrine gland secretions:

• Proteins, lipids, and steroids

Contaminants:

• Dirt, grease, blood, or other transferred substances.

The chemical make-up of the residue determines which development method (physical or chemical) will be most effective.

Physical methods rely on the physical adherence of developing agents to the moisture, oils, and residues of a latent print.

1. Powder Dusting Method:

• Fine powders are applied with a soft brush.
• Powder adheres to the sticky/oily residue.
• Types of powders:
  • Regular powders: black, grey, white (chosen for contrast with the surface).
  • Metallic powders: aluminium, bronze.
  • Fluorescent powders: viewed under UV/laser light.
  • Magnetic powders: applied with a magnetic wand, ideal for delicate surfaces.

2. Small Particle Reagent (SPR):

• A suspension of molybdenum disulfide that adheres to the fatty components.
• Used on wet or non-porous surfaces.

3. Vacuum Metal Deposition (VMD):

• Gold and zinc are evaporated in a vacuum chamber and deposit on the print.
• Highly sensitive for non-porous surfaces like plastics.

Advantages: Quick, inexpensive, and suitable for non-porous surfaces (glass, metal, plastic).

Limitations: Less effective on porous or textured surfaces and older prints.

Chemical methods react with specific components of the fingerprint residue to produce a visible or fluorescent product.

1. Ninhydrin:

• Reacts with amino acids in the residue.
• Produces a purple-blue color known as Ruhemann's Purple.
• Best for porous surfaces like paper and cardboard.

2. Iodine Fuming:

• Iodine vapors are absorbed by the fatty/oily components.
• Produces a temporary yellow-brown print; must be fixed or photographed quickly.

3. Silver Nitrate:

• Reacts with sodium chloride (salt) in the residue to form silver chloride.
• On exposure to light, it turns dark (metallic silver), revealing the print.

4. Cyanoacrylate (Super Glue) Fuming:

• Fumes polymerize on the moisture and residue, forming a white, stable print.
• Ideal for non-porous surfaces; can be enhanced with dyes.

5. DFO (1,8-Diazafluoren-9-one):

• Reacts with amino acids to produce fluorescent prints, more sensitive than ninhydrin.

Chemical methods are chosen based on surface type and the residue component targeted.

Principle:

• Ninhydrin reacts chemically with the amino acids present in the eccrine secretions of a latent print.
• The reaction yields a deep purple-blue compound called Ruhemann's Purple, making the print visible.

Procedure:

1. Prepare a ninhydrin working solution (dissolved in a solvent such as acetone or petroleum ether).
2. Dip, spray, or brush the solution onto the porous surface (paper, cardboard).
3. Allow the surface to dry.
4. Accelerate development using gentle heat and humidity (e.g., a heat press or humidity chamber at ~80°C, 65% humidity).
5. Purple ridges appear over several minutes to hours.
6. Photograph the developed prints promptly.

Applications:

• Ideal for porous surfaces.
• Can develop prints that are weeks or months old.

Advantages:

• Highly sensitive to amino acids.
• Prints can be further enhanced with metal salts (zinc/cadmium) for fluorescence.

Limitation: Not suitable for wet or non-porous surfaces.

Cyanoacrylate Fuming Method:

Principle:

• Cyanoacrylate (super glue) vapors polymerize upon contact with the moisture, amino acids, and other components of the latent residue, forming a hard, white, stable polymer along the ridges.

Procedure:

1. Place the evidence item in an airtight fuming chamber.
2. Heat a small amount of cyanoacrylate in a dish to generate fumes.
3. Maintain humidity (~80%) to promote polymerization.
4. Fumes deposit selectively on the print, producing a white ridge detail.
5. Enhance with fluorescent dyes (e.g., Rhodamine 6G, Basic Yellow 40) for better visualization.

Effectiveness on Non-Porous Surfaces:

• Non-porous surfaces (glass, plastic, metal) retain the residue on the surface rather than absorbing it.
• The polymerized print is durable and stable, resistant to smudging and handling.
• It fixes the print, allowing subsequent enhancement and long-term preservation.

Advantages: Stable results, works on difficult surfaces, allows further dye staining.

Comparison of Physical vs. Chemical Methods:

Key Considerations:

• Sequence matters: Physical (non-destructive) methods are usually applied before chemical methods.
• The surface type and residue composition dictate the choice.
• Fluorescent techniques may follow both for enhancement.

Both categories complement each other in a systematic development sequence.

Ridge characteristics, also called minutiae or Galton details, are the specific points where ridges deviate. They form the basis of individualization.

Major Minutiae Types:

• Ridge Ending: A ridge that abruptly terminates.
• Bifurcation: A single ridge splitting into two.
• Dot (Island): A very short ridge appearing as a dot.
• Enclosure (Lake): A ridge that bifurcates and then rejoins, enclosing a space.
• Short Ridge: A brief ridge segment.
• Bridge: A short ridge connecting two parallel ridges.
• Spur (Hook): A bifurcation with one short branch.
• Crossover: Two ridges crossing each other.

Importance in Identification:

• The type, location, direction, and relationship between minutiae are compared between a known and questioned print.
• A sufficient number of matching minutiae (points of similarity) with no unexplained differences establishes identity.
• Modern AFIS systems store and match minutiae coordinates automatically.

Minutiae are permanent and unique, forming the scientific foundation of fingerprint comparison.

Iodine Fuming Method:

Principle:

• Iodine crystals sublime to produce violet vapors.
• These vapors are physically absorbed by the fatty and oily components of the fingerprint residue, producing a temporary yellow-brown image.

Procedure:

1. Place the evidence and iodine crystals in a closed fuming cabinet (or use a fuming gun).
2. Gently heat the crystals to generate vapors.
3. Vapors settle on the print, revealing brown-colored ridges.
4. Fix the print quickly, as the image fades, using a fixative such as starch solution or 7,8-benzoflavone (which turns the print blue and stabilizes it).
5. Photograph immediately.

Applications:

• Suitable for paper, cardboard, and some non-porous surfaces.

Limitations:

• The developed print is temporary and fades rapidly if not fixed.
• Iodine vapors are corrosive and toxic, requiring careful handling.
• Less sensitive for older prints as fatty residue diminishes over time.
• Should generally be used first in a sequence, as it is non-destructive.

Secondary Classification further subdivides the primary classification groups based on the pattern types of the index fingers and, when needed, other fingers.

Capital Letter Group:

• Based on the pattern of the index fingers of both hands.
• Symbols used:
  • A = Arch
  • T = Tented Arch
  • R = Radial Loop
  • U = Ulnar Loop
  • W = Whorl
• The right index appears as the numerator, left index as the denominator.

Small Letter Group:

• When arches (a), tented arches (t), or radial loops (r) appear in the thumb, middle, or ring fingers, they are indicated by small letters.
• These small letters are written before or after the capital letter to indicate the exact finger position.

Purpose:

• Provides finer subdivision within primary groups.
• Improves filing accuracy and speeds up record retrieval.

Secondary classification, along with sub-secondary and final classifications, forms a complete Henry classification formula.

The sequence of development is critical because each technique may alter or destroy the residue, affecting subsequent methods.

General Principles of Sequencing:

• Non-destructive before destructive: Techniques that preserve the print are applied first.
• Optical/Visual examination first: Examine under normal and alternate light sources (UV, laser) before any physical/chemical treatment.

Typical Sequence for Non-Porous Surfaces:

1. Visual/optical examination
2. Cyanoacrylate (super glue) fuming
3. Fluorescent dye staining
4. Powder dusting (if needed)

Typical Sequence for Porous Surfaces (e.g., paper):

1. Visual/optical examination
2. Iodine fuming (physical, non-destructive)
3. DFO (fluorescent, before ninhydrin)
4. Ninhydrin (reacts with amino acids)
5. Silver nitrate (reacts with salts — last, as it is destructive)

Importance:

• Ensures maximum recovery of ridge detail.
• Prevents premature destruction of the print.
• Different reagents target different components, so ordering maximizes total information obtained.

A logical sequence therefore preserves evidentiary value and increases the chance of a usable print.

Ridge Count (used for Loops):

• The number of ridges intervening between the delta and the core.
• Procedure:
  • Draw an imaginary line from the delta to the core.
  • Count every ridge that touches or crosses this line.
  • The delta and core are not counted.
  • A single dot counts as one ridge; a bifurcation opening toward the line may count as two.

Ridge Tracing (used for Whorls):

• Determines the relationship between the two deltas of a whorl.
• Procedure:
  • Begin at the left delta and trace the ridge flowing from it toward the right delta.
  • Observe where the traced ridge ends relative to the right delta.
  • Count ridges between the tracing ridge and the right delta.
• Classification of tracing:
  • Inner (I): 3 or more ridges inside (above) the right delta.
  • Outer (O): 3 or more ridges outside (below) the right delta.
  • Meeting (M): fewer than 3 ridges on either side.

Purpose: Ridge counting and tracing provide numerical/positional data essential for sub-secondary classification.

Silver Nitrate Method:

Principle:

• Latent print residue contains sodium chloride (common salt) from perspiration.
• Silver nitrate () reacts with the chloride to form silver chloride ():
  
• On exposure to light (UV or strong sunlight), silver chloride decomposes to metallic silver, which appears dark grey/black, revealing the ridges.

Procedure:

1. Prepare a silver nitrate solution (typically 3–5% in water or alcohol).
2. Immerse or spray the porous surface.
3. Dry in darkness.
4. Expose to a strong light source until dark ridges appear.
5. Photograph promptly.

Precautions:

• Handle in the dark until ready for development, as premature light exposure darkens the whole surface.
• Silver nitrate stains skin and clothing; wear gloves and protective clothing.
• Photograph quickly because prolonged light causes the background to darken, reducing contrast.
• Being destructive, it is applied last in the porous-surface sequence.

Application: Effective on porous surfaces like paper and wood.

Fingerprint identification rests on three scientifically established principles:

1. Individuality (Uniqueness):

• No two fingerprints, even from the same individual or identical twins, are exactly alike.
• The random formation of friction ridges during fetal development ensures uniqueness.

2. Permanence (Persistence):

• Ridge patterns are formed before birth and remain unchanged throughout life.
• Only superficial injuries heal without altering the pattern; deep scars that damage the dermis may leave permanent identifiable scars but do not create a duplicate pattern.
• The pattern only changes in size, not in ridge detail.

3. Classifiability:

• Fingerprints can be systematically classified (e.g., into arches, loops, whorls) and filed, allowing efficient storage and retrieval.

Supporting Concepts:

• Persistence was demonstrated through long-term studies of the same individuals.
• These principles are upheld by courts worldwide, making fingerprints one of the most reliable and legally accepted forms of identification.

Together, these premises justify the use of fingerprints in forensic and civil identification systems.