The forensic use of
bioinformation
Forensic bioinformation
Includes…
• Fingerprints
• DNA
Fingerprinting
•The fingerprint is the most commonly used
method of identification
•No two people have the same fingerprints
(including identical twins)
•Fingerprints develop before birth and remain
unchanged throughout life
•Identification relies on the matching of
patterns and the detection of certain ridge
characteristics (Galton details)
DNA sample
• From a person – a biological sample taken
from an individual, usually a swab from the
inside of a person’s cheek
• From the crime scene - samples of
biological material found at a crime scene
that may be taken by scene of crime officers
include blood, skin cells, semen, hair etc
DNA profiling
• DNA from a sample is extracted, analysed
and catalogued.
• Sections of DNA are analysed for the
presence of particular ‘markers’
• A DNA profile is a sequence of 20
numbers determined by these ‘markers’
DNA Profile
A DNA profile
•
Contains genetic information to help identify
a person
•
On average, the chance of another
(unrelated) person sharing the same 20
number profile as you is around one in a
billion
How is bioinformation used by
police?
.
Arrest
Fingerprints and a DNA sample are taken
Fingerprints are
sent to NAFIS
(National
Automated
Fingerprint
Identification
System) for
checking
A DNA profile is
constructed from the
sample – the profile is
stored on the National
DNA Database (NDNAD)
The sample is kept in a
fridge
Police check fingerprints and DNA
profiles against crime scene
samples from unsolved crimes
If the DNA profile or fingerprint of
a person matches a crime scene
sample, this may be used as
evidence in court that the person
was involved in the crime
However….
Finding a persons DNA
or fingerprint at a crime
scene does not
necessarily prove that
they were involved in the
offence…
• It could have been planted at the scene,
carried there on an object, or been transferred
there via someone else’s clothing or shoes
• The person may have been at the crime
scene legitimately (e.g. they live there) or
could be a witness/victim
Using DNA evidence in court
• DNA profiling is generally
a very reliable way of
identifying a person
BUT…
• If a crime scene sample contains only tiny
amounts of DNA, this can sometimes make
the DNA profiling less reliable
• DNA evidence in court is presented as
statistics which can be confusing for people in
the courtroom, including members of the jury
• DNA can be contaminated before, during, or
after the police and laboratory staff collect it
and use it – care must be taken to try and
avoid contamination
Using fingerprint evidence in
court
• Fingerprints are hard to analyse and trained
experts must check them
• Partial fingerprints are even
harder to analyse
• When fingerprint evidence in used in court,
juries must be aware that when a match is
declared, it is never a matter of scientific
certainty or conclusive fact; it is the opinion of
the expert
The forensic use of
bioinformation
quiz
For each of the following statements
you must work out the missing word
Question 1
No two people, even identical
twins, have been found to have
the same ____________?
Question 2
A DNA profile is recorded on
the National DNA Database as
a sequence of ______?
numbers
Question 3
Fingerprints are stored on a
database called ___________?
Question 4
On average the chances of two
people sharing the same complete
DNA profile is around one in a
____________?
Question 5
A DNA ____________? is a
biological substance such as
blood, skin, hair or semen