Download SEMEN INFORMATION SHEET

Centre of Forensic Sciences
Biology Section
Centre of Forensic Sciences
Investigators & Submitters
Technical Information Sheets
SEMEN INFORMATION
A.
INTRODUCTION
Semen is a liquid from the male reproductive system that usually contains spermatozoa
(sperm cells) along with various other substances. Mature males emit semen during
ejaculation. The spermatozoon (singular of spermatozoa) is the male reproductive cell.
Human semen usually contains high levels of a substance called acid phosphatase. Acid
phosphatase has a chemical activity, which allows for its detection. Human semen also
contains high levels of a substance called p30, which, with few exceptions, is specific to
semen.
B.
EXAMINATION FOR THE PRESENCE OF SEMEN
In general, the following steps are taken to determine whether or not semen is present on
an item. Semen is first located by means of a visual examination and acid phosphatase
testing. Microscopic identification of sperm cells or the detection of p30 confirms the
presence of semen.
C.
TESTS FOR THE PRESENCE OF SEMEN
Visual examination
May involve the use of a stereomicroscope (a magnifying
tool) and enhanced light sources.
Acid phosphatase testing The presence of acid phosphatase on an item will give rise
to a purple coloration upon addition of specific chemicals.
The intensity of the color produced relates to the quantity of
acid phosphatase present.
Testing for p30
The liquid component from an extract of cellular material
may be tested for the presence of p30. The detection of p30
is done using a commercially prepared reagent that
specifically binds p30, allowing for its visual detection.
Effective: January 6, 2005
Authorized: R. Frappier, DNA Technical Manager
Semen Information
Page 1 of 3
Centre of Forensic Sciences
Microscopic examination
D.
E.
Biology Section
Human sperm cells are identified in an extract of cellular
material. Criteria for human sperm cell identification are as
follows: size, shape and staining properties, following a
treatment with chemical dyes.
LIMITATIONS
1.
Semen is lost from body cavities in a variety of ways. The maximum reported time
periods at which semen has persisted in living persons is as follows: 7 days in the
vagina, 1 day in the mouth, 2 to 3 days in the anus/rectum. Generally, semen will not
persist for these maximum time periods.
2.
The presence of spermatozoa on anal/rectal samples does not always indicate that
anal/rectal intercourse has occurred.
3.
The non-detection of semen on internal samples is not in itself proof that a sexual act
did not occur.
4.
The detection of strong acid phosphatase activity alone is not proof of the presence
of human semen. Acid phosphatase is also found in other body fluids at lower levels.
Post-mortem internal samples, heavy vaginal deposits, feces, urine, unusually high
numbers of bacteria or yeast, plant extracts and certain chemicals may all show
various levels of acid phosphatase activity.
5.
Acid phosphatase and p30 are water-soluble and can therefore be lost through
contact with water e.g. laundering. Small numbers of spermatozoa can be retained
on fabric after laundering.
6.
The presence of high levels of p30, with few exceptions, is specific to semen. The
levels of p30 reported in the literature for other body fluids are comparatively very
low, although high levels of p30 have been found in the serum of prostatic cancer
patients and in rare instances in semen-free vaginal swabs.
7.
It is possible for a small number of spermatozoa to be deposited on items through
innocuous means such as secondary (indirect) contact or laundering.
GLOSSARY
Ejaculation
An abrupt discharge of semen.
Pre-ejaculatory fluid
A small quantity of lubricating fluid, released prior to
ejaculation that may or may not contain small numbers of
spermatozoa.
Time Since Intercourse (TSI)
An estimate of the maximum time elapsed between
intercourse and the collection of internal samples.
Effective: January 6, 2005
Authorized: R. Frappier, DNA Technical Manager
Semen Information
Page 2 of 3
Centre of Forensic Sciences
Biology Section
Vaginal/Oral/Rectal smear
A smear made from a vaginal/oral/rectal swab onto a
microscope slide.
Vasectomy
A medical procedure performed in order to prevent the
emission of spermatozoa during ejaculation. Commonly
used for male sterilization.
Effective: January 6, 2005
Authorized: R. Frappier, DNA Technical Manager
Semen Information
Page 3 of 3