Investigating CSI – Background material Table of Contents I ...

II. Tools and Techniques for DNA Forensic Science
A. Detection of Body Fluids
Ultraviolet Light Illumination
Short wave 254nm/Long wave 365 nm
The use of ultraviolet (UV) light can be of great assistance in many forms of
forensic investigation. Since body fluids like semen, saliva, perspiration and
vaginal fluids are naturally fluorescent, the use of a UV light source offers a
unique method for locating these stains. The dried bodily fluids will naturally
fluoresce when illuminated with UV light source. We can then isolate the exact
location of the stain(s) to test, instead of testing the entire, large pieces of
evidence such as a mattress, a carpet, a sheet, an article of clothing, etc.
Microscopy
Individual sperm heads can be accurately identified based on their morphological
characteristics, using a phase contrast microscope and 20–100x magnification.
An ideal, mature spermatozoon has an oval shaped head with a regular contour
(4.0-5.0 um long and 2.5-3.5 um wide) with a pale anterior part (acrosome; 40-
70% of the head area) and a darker posterior region. The length-to-width ratio of
the head should be 1.50 to 1.75. The sperm tail should be attached in a
symmetrically situated fossa in the base of the head. The base of the head
should be broad and not arrow-like. Only one tail should be attached (about 45
um long), not coiled, nicked or bent over itself. Immediately behind the head the
first part of the tail, the mid piece, should be somewhat thicker (maximum width =
1 µm) and about 7-8 um long.
Source: http://www.dnatesting.biz/Semen_Sperm_ID/semen_sperm_id.html
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