FORENSIC INVESTIGATION

 Introduction to Body Fluids and DNA Techniques

Instructions to students

Part A of this document once completed constitutes, 25% of the module marks. This document consists of five sections each containing 3 questions.

  1. Part B of the Laboratory Report once completed constitutes 25% of the module marks.
  2. For the above 2 documents, totaling 50% of the module marks, you must evidence the following module learning outcomes:
  3. Apply various presumptive tests to samples from crime scenes to determine whether or not they are body fluids.
  4. Demonstrate the correct use of DNA methodologies.

This proforma can be read in conjunction with the Marking Scheme.

Section 1: Body Fluids Recovery

Scenario

Body fluids can be present at many crime scenes and they can be of critical importance to the identification of an offender and to the understanding of the circumstances of the incident. Knowing how to record and recover these fluids correctly is vital if the evidence is to maintain its integrity and be suitable for court.

The following questions will test your understanding of the recovery methods used and their importance. You should use in text referencing where appropriate.

  1. What body fluids are most commonly found at crime scenes and how might they assist an investigation?
  2. Swabbing is the most common technique used to recover body fluids, but how is this technique carried out? Consider equipment used (including PPE), the actual process of recovery, and the subsequent packaging and storage of the sample.
  3. Considering your answer to question 2 above, why is it important for consistency to be applied across all forensic services carrying out this technique? In your answer consider how this consistency is governed and what is in place to ensure that correct practice is adhered to.

Section 2: Presumptive Testing of Body Fluids

Scenario

Having an indication of what the source of a particular body fluid is at a scene can provide useful information to an investigation. It can not only assist with the subsequent recovery strategy but also build a picture of the events that lead to that fluid being present. There are a variety of presumptive tests available that can indicate the presence of particular fluids.

These questions will explore your knowledge of presumptive testing and allow you to demonstrate your research skills. You should use in-text referencing where appropriate.

  1. A red stain has been found at a crime scene and the Crime Scene Investigator suspects it may be blood. What tests are commonly available at scenes to indicate to the CSI that the stain could be blood. Give a brief description of how these tests are carried out.
  2. Luminol is a chemiluminescence test that was first discovered in the 1930s. What is Luminol and how might it provide advantages over any other tests you mentioned in your answer to question 1?
  3. Presumptive testing can be a very useful tool in the early stages of an investigation. However, it can cause issues in some circumstances and may lead to some uncertainty over the origin of a sample. Evaluate the use of presumptive testing at crime scenes and consider both advantages and disadvantages of the techniques.

Section 3: Blood Pattern Analysis

Scenario

BPA is an important investigative tool carried out by Forensic Biologists at crime scenes to give information as to how a crime may have been perpetrated. It is a time consuming process, using the expertise of the scientist and rigorous recording and recovery methods to establish certain events that may have occurred at the time of the incident.

The following questions will use your knowledge gained from lectures and practical sessions and will also require you to research the subject of Blood Pattern Analysis. You should use in-text referencing where appropriate.

  1. Describe the main types of blood patterns that can be found at crime scenes and what these different patterns may indicate.
  2. Being able to calculate the angle of impact of multiple bloodstains can lead to a point of origin for those bloodstains being determined. Calculate the angle of impact for the two stains shown below and show your calculations for how you arrived at the result.
  3. Besides determining a point of origin based upon the angle of impact of blood spatter it would often be useful to know from what height a drop of blood has fallen from. Is it possible to determine this? Explain your answer fully.

Section 4: Use of Markers

Scenario

There are approximately 3 billion base pairs of DNA in the human genome. Only ~1% of this genome can be characterized as ‘gene’ or ‘protein coding’, which leaves 99% mainly unaccountable. Previously termed ‘Junk DNA’ (non-coding DNA is a slightly friendlier term), this 99% is becoming more and more important as research continues, and we now know that this non-coding DNA is composed of regulatory sequences, introns, pseudogenes, and repeat sequences. It is in these repeat sequences where we can find the variability between individuals that can lead to a positive identification. But where in this 99% to look? This is where DNA markers can be utilised.

The following questions will test your research skills and your understanding of the use of different DNA markers. You should use in-text referencing where appropriate.

  1. Compare and contrast VNTRs and STRs with respect to forensic science.
  2. Using your research skills, produce a table showing the loci that are currently amplified using DNA-17. You should also include the chromosomal location and sequence of the loci. The correct format should be used.
  3. Using your knowledge of Population Genetics and Linkage Disequilibrium, discuss the importance of using marker SE33 when carrying out DNA profiling.

Section 5: DNA Fingerprinting

Scenario

DNA Profiling is the colloquial term used when referring to a DNA profile of an individual, using the markers described in section 4. Different methods and visualisation techniques are used to analyse the markers described. Most now use PCR based systems where segments from either side of the loci are amplified, the products are then analysed using Capillary Electrophoresis to provide repeat numbers – e.g. the DNA Profile.

In this exercise, you will have to analyse data provided from a profile and make inferences about the data.

  1. Describe the process of Capillary Electrophoresis. You may include self-produced images in your answer.
  2. Using the ladder provided in the appendix, provide a profile for the Fingerprint below.
  3. A 15-year-old female has claimed that her father has sexually assaulted her, which has resulted in a pregnancy. The father was arrested and charged with incestuous paedophilia and sexual assault. The father denied all claims and stated that his daughter was sexually active with her 18-year-old boyfriend. To establish a genetic profile of the foetus, chorionic villus sampling was utilised. Samples were collected from the mother, boyfriend, and the alleged father of the foetus. STR profiling was utilised with the following results:

 

 

Locus

 Mother Unborn child 18 year old boyfriend Alleged Father
FGA 21,23 22,23 21,22 20,22
TPOX 8,10 8,11 11,11 11,11
D8S1179 12,13 12,13 13,13 13,13
vWA 14,18 14,15 17,18 14,15
Penta E 10,11 11,16 10,11 14,16
D18S51 13,14 14,14 14,17 14,17
D21S11 31.2,32.2 30,32.2 30,30 29,30
TH01 6,9 6,9.3 5,6 6,9.3
D3S1358 16,17 16,17 15,15 15,17
Penta D 11,14 11,11 11,14 11,12
CSF1PO 8,12 8,12 8,11 12,12
D16S539 11,13 9,11 9,13 9,10
D7S820 9,10 8,9 8,8 8,9
D13S317 11,12 10,11 7,12 10,13
D5S818 7,8 7,11 11,12 11,12
Amelogenin XX XX XY XY

 

Analyse the data and determine whether the girl’s father or the boyfriend is the father of the unborn child. Justify your answer.