biological evidence - body fluids

semen

important evidence in sexual assault cases, presumptive and confirmatory tests available, important source of dna

acid phosphatase AP test

is an enzyme present in high quantities in semen and is quite stable, substrate - alpha naphthyl phosphate, the acid cuts up phosphate dephosphorylates naphty phosphate, alpha naphthyl binds to fast blue B dye, turns purple in presence of acidic solution, presumptive test as other biological material has AP, sensitive not specific to semen test can give false postive

semen testing using PSA - prostate specific antigen

protein called p30 also psa was discovered 1970 no longer used, antibodies Ab against PSA are commerically available, used in precipitation test where semen extract and Ab form visible precipitation line between

semen cells

called spermatozoa unique to semen so identification microscopilcally can confirm presence of semen, stained material is immersed in small amount of water, rapid stirring of liquid transfers some sperm to water, stains added called christmas tree stain, sperm head turns red and tail turns green, if there is no tail the acrsome will be pink whereas a epithelical cell would be all red

absence of sperm

medical condition, low sperm count (oligospermia), no sperm present (aspermia), vascetomies, extremely brittle when dried, so not easy to find, survival of spermatozoa in a living person is affected by location and activites of individual.

persistence of semen

can be found in vagina 24 hours after ejaculation but can be found up to 48 hours max 4 days, shorter persistence of semen in anal intercourse, can survive in mouth up to 24 hours, can survive longer periods in deceased bodies, may persist on clothing if not washed

semen as DNA source

need to sperate sperm dna from other dna, swabbed materials from a rape evidence kit may contain non sperm cells from victim as well as rapist, differential extraction is performed involving the lysis of the nonsperm cells followed by centrifugation to remove the still intact sperm cells

saliva

useful dna source, epithelial cells present, can be transffered by spitting, mouth direct contact, saliva may yield dna profile from sexual assault case

test for saliva

the phadebas amylase test presumptive test to detect alpha-amylase an enzyme present in high concentrations in human saliva, if amylase present it breaks down walls of beads releasing blue dye into solution, activity can be measured using a spectrophotometer or visualised on reagent coated paper

vomit

no test, odour and appearance, dna profiling successful as cells from stomach may come up

urine

not good for dna, urea and creatinine, urine stains low yield a dna profile because of low level of cells present, chance of getting some from a liquid sample, presumptibe test based on presence of high urea and creatinine

faeces

a test for presence of urobilinogen in faeces, dna profiling unsuccessful