Biological Evidence

Hair Evidence

• Hairs usefulness when solving a crime is very limited (poor discriminatory power)

• Not possible to determine if hair originated from a particular person based on physical appearance or morphology

• When hair obtained from root = valuable evidence

Sample required for hair analysis

• Items searched for hair including clothing, balaclavas and motorcycle helmet

Morphology of hair layers

Cuticle, cortex, medulla

Cuticle

The outer layer covering the hair. Resistant to chemical decomposition and retains its structural features over a long period of time. Made of scales that point to the tip of the hair.

Method to see the cuticle

scanning electron microscopy (SEM)

Cortext

Layer of cells within the cuticle. Contains the pigment granules (give hair color)

Method to see cortext

Examined microscopically in a liquid medium to allow light to penetrate hair

Medulla

Collection of cells that look like a central canal running through hair. For animals diameter more than ½ hair, in humans its less than 1/3. In human hair medulla fragment is absent

Hair root

Shape and size determined by growth phase of hair

Follicular tag

translucent piece of tissue surrounding the hair’s shaft near the root

Phases of hair

Anagen, catagen, telogen phase

Anagen phase

Initial growth phase, when follicle produces hair root. Can last up to 6 years, when hair is pulled from the root some hairs in anagen phase have a follicular tag (DNA can be extracted)

Catagen

Hair growth rate decreasing. 2-3 weeks root bulb shrinks as it is being pushed out of follicle

Telogen

Hair growth has ended and root takes on club shaped appearance. 2-6 months hair pushed out of follicle and sheds

Natural shedding

Hair in telogen phase, poor for DNA typing

Forcibly pulled

Hair collected from scenes often yield a DNA profile

Mitochondrial DNA

Hair shaft can also be used where genomic DNA is limited

How many full length hairs from head is needed for a sample

50

Serology

Scientific study of blood serum and other bodily fluids

Serum

blood is allowed to clot then liquid fraction

Blood components

red blood cells, white cells, platelets and plasma

Blood typing

blood grouping was used with other serotyping methods to partially individualize a blood sample based on non-DNA genetic markers

Red blood cells

Carry oxygen around body but also have structures on cell surface known as antigen

Antigen

proteins made from the DNA inherited from our parents

ABO blood typing

• Type A has A antigens on cell surface

• Type B has B antigens on cell surface

• Type AB have both A and B antigens

• Type O have neither

Agglutination

Each AB can attach to different RBC so a network of cross-linked cells is created

Most common blood group world wide

O (46%)

Semen:

• Important in SA cases

• presumptive and confirmatory tests available

• important source of DNA identification

Acid Phosphatase

enzyme present in high quantities in semen and is quite stable.

Testing Methods for Semen

Fast Blue B dye, MUP,PSA

Fast Blue B dye

Turns purple in the presence of acidic solution and Fast Blue B dye. Moistened filter paper pressed on item and test solution added.

Methyl umbelliferyl phosphate

uses fluoresces under UV when it comes in contact with AP

PSA

used in precipitation test where semen extract and AB form visible precipitation line between

Spermatozoa

unique to semen identification. Microscopic presence of semen confirmed

Spermatozoa test

• Stained material is immersed in small amount of water, rapid stirring of liquid transfers some sperm to water

• Drop placed onto slide and observed under microscope

Persistence of semen

• Spermatozoa should be found in the vagina 24 hours after, sometimes 48 hours and some cases up to 4 days later

• Shorter persistence for semen deposited in the anal intercourse

• Spermatozoa can survive 24 hours orally

• Can survive in deceased bodies, for longer in cool temperatures

• Can last indefinitely on clothing which has not been washed and kept in dry environment

Differential extraction

Performed involving the lysis of the non - sperm cells followed by centrifugation to remove the still intact sperm

Semen as a DNA source

In order to perform DNA typing on sperm, it needs to be separate the sperm DNA from any other DNA

Phadebas Amylase Test

• Detects the presence of alpha - amylase, if present a blue dye is released into solution.

• Amylase can be measured alternatively, with a spectrophometer or visualized on reagent-coated paper

Vomit

• No specific test to identify

• Characteristics such as odor, appearance of sample

• DNA profiling usually successful on both bulk vomit and dry stains

Urine

• Useful during investigation and often not visible

• Tests relatively insensitive due to dilution of its constituent characteristics urea and creatinine

• Unlikely to yield DNA because low presence of cells in fluid

• Small chance of getting DNA when concentrate enough cells from a large area of volume

Feces

• Test can be carried out to indicate presence of urobilinogen

• DNA profiling usually unsuccessful

• Swab of surface of the formed stool is required before attempting DNA analysis