Biological Evidence - Bodily fluids

enzyme present in semen in high quantities

acid phosphatase AP

what colour does semen turn in the presence of acidic solution and fast blue b dye

purple

reagent that fluoresces under UV when it comes in contact with AP in semen when sprayed onto filter paper or directly onto garment

MUP - methyl umbelliferyl phosphate

semen testing using PSA

A protein called p30 also known as prostate specific antigen PSA was discovered

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

Antibodies Ab against PSA are commercially available

sperm cells are called

spermatozoa

they confirm the presence of semen

oldest confirmatory test

presence of semen

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

drop placed onto a slide and observed under microscope

absence of sperm

medical condition with low sperm count - oligospermia

no sperm produced - aspermia

vasectomies

absence of semen in sexual assault cases

does not meant hat sexual activity did not take place, intercourse without ejaculation is not unusual

survival of spermatozoa in a living person is affected by

the location on the body

the activities of the individual after sexual activity

persistence of semen

spermatozoa should be found in vagina 24 hours after ejaculation - likely to be found up to 48 hours - rarely found four days later

shorter persistence time for semen deposited in anal intercourse

spermatozoa may survive in the mouth up to 24 hours after oral ejaculation

spermatozoa may survive for longer periods in deceased bodies - especially in cool environments

persists indefinitely on clothing which has not been washed and kept in a dry environment

semen as DNA source

in order to perform DNA typing on sperm DNA, its desirable to separate the sperm DNA from any other DNA present

in swabbed materials from rape evidence kit, the swabs may contain non sperm cells from the victim as well as sperm cells from the rapist

differential extraction - semen as DNA source

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

saliva is a useful source of DNA

DNA present in epithelial cells that transfer from the lining of the mouth cavity to the liquid secreted from the salivary glands in the mouth

saliva can be transferred by

spitting

mouth coming into direct contact with objects such as cigarettes, drinking straws, drinking utensils, food or balaclavas

in the course of kissing, sucking, licking or biting

in sexual assault cases where semen is not found, saliva may yield the DNA profile

presumptive test for saliva

the phadebas amylase test is used to detect the presence of alpha amylase - the enzyme present in high concentrations in human saliva

if amylase is present, a blue dye is released into solution

amylase activity can be measured

using a spectrophotometer or alternatively visualised on reagent coated paper

vomit

no specific test to identify vomit

characteristics such as odour and appearance of the sample allows a forensic scientist to determine the likelihood of it being vomit

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

Urine tests

relatively insensitive due to dilution of its constituents

characteristic constituents include urea and creatinine

tests for urine are unlikely to yield a DNA profile

because of the low level of cells present in the fluid

if a large volume of urine is found, it is possible to concentrate enough cells

urine sample taken from victim in rape cases

for drug toxicological analysis

urine is analysed for substances associated with drug facilitated sexual assaults - rohypnol

faeces test

a test can be carried out to indicate the presence of urobilinogen in faeces

DNA profiling of faeces is usually unsuccessful

a swab of the surface of the formed stool is required before attempting a DNA profile