Biology Reference
In-Depth Information
Figure 3.3
It is standard practice for scene of crime officers to wear full overalls, shoe covers,
gloves and face masks when collecting biological evidence from a scene of crime. Even with
these precautions it is possible for crimes to be contaminated by forensic investigators, and it
is becoming common for the DNA profiles of police officers and crime scene investigators to be
stored on a database; any profiles recovered from the scene of crime can be checked against this
elimination database to rule out the possibility of a profile coming from an investigating police or
crime scene officer
have been developed to enable crime scene investigators and forensic biologists to
utilize the inherent properties of biological evidence to both locate and character-
ize the material. When characterizing material there are two categories: presumptive
and confirmatory. A range of presumptive and confirmatory tests is available that
aids the identification of the three main body fluids encountered: blood, semen and
saliva. Ideally, tests should be safe, inexpensive, simple to carry out, use a very small
amount of the sample, be quick to perform and provide a simple indication of the
presence or absence of a body fluid. The test should not affect the ability to carry
out subsequent DNA profiling.
Presumptive tests can give false positives; however, in many circumstances, when
the type of biological material is not of critical importance for a case, a positive
result with a presumptive test will be sufficient information to move on to DNA
analysis - which itself acts a confirmatory test for human biological material. In other
circumstances, when the origin of the material is important, as is often the case with
offences of a sexual nature, a confirmatory test is required that will unambiguously
identify the biological material.
Blood
Blood is composed of liquid plasma, which contains soluble proteins, lipids, glu-
cose, hormones, metabolites and salts, and the cellular component - red blood cells
(erythrocytes), white blood cells (leucocytes) and platelets (thrombocytes).
