DNA profiling- Key words: Polymerase chain reaction, introns, exons, STR’s Starter: A big question “What is DNA profiling, and why is it used in forensics?”

DNA Profiling All pupils will: Recall the uses of DNA profiling. Most pupils will: Describe the method used to prepare a DNA profile. Some pupils will: Discuss the benefits of genetic profiling Skills: Communication, Problem Solving, WWO,

DNA is the single most important molecule in living cells

DNA are large molecules – You have about 9 MILLION KILOMETRES of DNA in your body

If you were to write down the codes for all the chemicals in your DNA it would fill about 200 phone books – about 3 billion letters

DNA Profiling 1987 – Forensic scientist first used DNA profiling (genetic profiling) to solve a rape case The chemical structure of everyone's DNA is the same - the only difference is the order of the base pairs and every person has a different sequence.

How it works Only 0.1% of DNA differs from one person to the next. These differences are used to generate a DNA profile (from blood, bone, hair, or other body tissues) Enzymes are used to cut out specific sequences of DNA. Sequences are arranged in order of length using electrophoresis. They are labelled so that they show up when photographed.

DNA fingerprint Forensic comparison Which sample matches the blood stain? Sample A Sample B

Activity 1 Suppose the following are DNA samples of a couple who plan on having children. Give a possible DNA coding for two of their children. Mum Dad 1 2

Mum Dad 1 2 Mum Dad 1 2 Mum Dad 1 2 Mum Dad 1 2 Mum Dad 1 2 Mum Dad 1 2

Activity 2 Here are six different DNA tests. Suppose these DNA tests are of a couple who are married and their possible children. Which of the kids belong to both parents? Which of the kids belong to only the mother? Which of the kids belong to only the father? Which of the kids belong to neither parent?

Mum Dad 1 2 3 4

Mum Dad 1 2 3 4 Mum Dad 1 2 3 4 Mum Dad 1 2 3 4 Mum Dad 1 2 3 4

Gene Ownership – A National Database Britain has the largest DNA database of its citizens in the world. It holds details of over 4 million people – 5.2% of the UK population These include people who have been found guilty of a crime as well as those suspected of a crime but eventually cleared. Should there be a database?

Activity In pairs think of as many arguments in favour of having a National database of DNA profiles and arguments against.

Arguments in favour Each person's DNA is unique so, DNA evidence collected from a crime scene can implicate or eliminate a suspect (like fingerprints) It also can analyse unidentified remains through comparisons with DNA from relatives When evidence from one crime scenes are compared, there may be a link to the same perpetrator, so helping to solve crimes If biological evidence from crime scenes is collected and stored properly, forensically valuable DNA, that may be decades old, could help solve an unsolved crime

Arguments against It is possible for an innocent person’s DNA to be planted at a crime scene An innocent person’s DNA may also be at a crime scene even though they weren’t involved in the crime High cost to maintain and develop the database It invades our right to privacy. The data might get into the hands of  commercial companies such as insurance, loan and employers.  If it were used to identify that you had a genetic risk for a serious disease, could you find yourself refused life insurance, a loan, or even a job? http://www.bbc.co.uk/learningzone/clips/dna-database-legal-or-illegal/8463.html

Question Explain what is meant by ‘genetic profiling’, including its uses and the advantages and disadvantages associated with it. (6 Marks)

Answer…. Genetic profiling is where DNA is analysed to show a DNA ‘pattern’ That is specific to an individual DNA is cut into smaller pieces and separated by electrophoresis Pattern is compared to other samples Uses (any two): Paternity, criminal cases, familial connections Advantages (any one): Matching parents to children, genetic screening, providing evidence for criminal cases Disadvantages: (any one): Insurance rejections, not 100% accurate, invasion of privacy, affect chances of finding a job,

Keywords Specific DNA Profiles, Electrophoresis, Genetics Criminal Paternity Analysed

DNA – True or False? http://www.teachers.tv/videos/dna

The big picture: “How is DNA profiling used in forensics?” Learning outcomes To explain how a DNA profile is made. To analyse the stages in the polymerase chain reaction (PCR). To evaluate the benefit of using PCR when producing a DNA profile.

What is DNA profiling? Also known as genetic or DNA fingerprinting. Relies on the fact that everyone’s DNA is different (except identical twins). Compares introns (non-coding regions) and exons (coding regions) within the DNA. Also compares repeated sequences within introns (known as short tandem repeats, STR’s for short).

An overview of the process… DNA profiling https://www.youtube.com/watch?v=ZxWXCT9w VoI An overview of the process…

How is a DNA profile made? A multi-stage process: 1: DNA sample extracted 2: DNA is amplified using PCR 3: Fragments of different lengths are produced by cutting up the DNA 4: The fragments are separated and visualised using gel electrophoresis.

DNA Profiling 1 2 Gel electrophoresis involves taking DNA samples, breaking them up into sections or genes, and then running them through a gel – the smaller genes mover faster so go further compared to larger ones. Seen in Fig’s 1 and 2. If you have two samples from the same person, then these sections of DNA, called bands in the gel, will appear in the same places when left to run for the same amount of time. See Fig 2 – Crime scene samples matches the sample from suspect 3. 3

DNA profiling is a technique that allows an individual’s genes to be visualised. This allows someone's genetic makeup to be compared to known genes to see if they too have them. This technique can be used to identify genetic disorders in individuals or match DNA samples to individuals. We usually sample regions of DNA called introns, once called Junk DNA, since it varies between individuals (but not twins). As opposed to exons (genes in the normal sense). These repetitive regions of ‘Junk DNA’ are now called STRs: Short Tandem Repeats. Genetic testing can be used for identifying genetic disorders or for identifying suspects in crimes. The blood stain bands match up to Johns – therefore it is his DNA. Alex Jeffreys’ first use of DNA Profiling: http://www.youtube.com/watch?v=Fz6p8EgJZ3w

Sources of DNA for Genetic Profiling These are sources of cells obtained where you can extract DNA from them for genetic testing.

How do we get the STRs from the DNA sample? You’ll need to macerate the sample and add enzymes to break down the cellular membranes. We’ll need to cut out the sequences of DNA we wish to compare, the STRs. Enzymes are perfect for this, specifically restriction enzymes (restriction endonucleases) which cut at designated DNA sequences.

Samples must be compared against possible sources Blood sample from crime scene Victims profile Suspects Profile

Is this man the father of the child? Mother Child Man The answer is yes. Remember, you are 50:50 your mother and father. So some of your genes will come from another parents. In this example, some bands of the child come from the Father, others from the Mother. Jeremy Kyle style.

Famous Cases Colin Pitchfork was arrested (1987) for the rape and murder of two girls in 1986. He was only caught, and then sentenced, in 1988 after DNA evidence came to light. Wikipedia - On 1 August 1987, one of Pitchfork's colleagues at the bakery, Ian Kelly, revealed to fellow workers in a Leicester pub that he had obtained £200[6] for giving a sample while masquerading as Pitchfork. Pitchfork told Kelly that he could not give blood under his own name because he had already given blood while pretending to be a friend of his who had wanted to avoid being harassed by police because of a youthful conviction for burglary. A woman who overheard the conversation reported it to police.

Famous Cases In 1994 O.J Simpson was cleared of murder charges which relied heavily on DNA evidence. The new technology, and the jury’s lack of confidence with it, formed a major part of the case. This was later parodied in SouthPark as the Chewbacca Defence – it has become a technical term. The Chewbacca Defence being a law tactic whereby the jury is presented with myriad facts or procedures they are unable to confidently understand the implications of – in the O.J Simpson case the jury was “bamboozled” and “blinded with science” in order to undermine their confidence in understanding DNA profiling. https://www.youtube.com/watch?v=clKi92j6eLE

The names along the right are blood samples – either stains from a location, or from suspects. #52 and #12 match to Simpsons genetic profile. Difficulties at the time in passing judgement included the jury’s poor understanding of this pioneering technology, what it’s result meant, and issues in race relations at the time of the trial. Criminologist Dr. Thomas O'Connor says that when DNA evidence shows "inclusion", that is, does not exonerate a client by exclusion from the DNA sample provided, "About the only thing you can do is attack the lab for its (lack of) quality assurance and proficiency testing, or use a 'Chewbacca defense' … and try to razzle-dazzle the jury about how complex and complicated the other side's evidence or probability estimates are."[4] Forensic scientist Erin Kenneally has argued that court challenges to digital evidence frequently use the Chewbacca defense by presenting multiple alternative explanations of forensic evidence obtained from computers and Internet providers to raise the reasonable doubt understood by a jury. https://www.youtube.com/watch?v=xwdba9C2G14

Old and modern forms of gene profile presentation. This is what genetic profiles will usually be presented as – on the left traditional – on the right, a clearer illustration. Each column is a sample with the genes all spread out having been seperated.

The big picture: “How can DNA profiling be used to solve a crime?” Learning outcomes To recap the key features of the polymerase chain reaction. To analyse the stages in gel electrophoresis and southern blotting. To evaluate the usefulness of this technique.

DNA profiling Once fragments of DNA have been produced (either through PCR or the uses of restriction enzymes) the fragments then need to be visualised. This is achieved using gel electrophoresis and southern blotting. Gel electrophoresis separates the fragments according to size on a agarose gel. The gel is fragile so the fragments are then transferred to a nylon membrane in a process known as southern blotting.

DNA profiling Fragments are added to the wells of an agarose gel. A current is passed through the gel, as DNA is negatively charged the DNA moves from negative to positive down the gel. Smaller fragments travel faster, so will move further down the gel in the same amount of time. Southern blotting then makes the banding pattern more stable- the DNA is transferred to a nylon/ nitrocellulose membrane to be viewed.

Tasks All: Draw a flow chart to explain how the fragments are visualised. Words to include: agarose gel, gel electrophoresis, negative charge, DNA probe, southern blotting Most: Explain what a DNA probe is, and why it is used in this process Some: Analyse what DNA profiling is used for, and how infallible it is (likely to give correct results)

Exam question

Peer assessment

PCR The polymerase chain reaction is used to copy a DNA sample many times. A visualisation of the process: https://www.youtube.com/watch?v=iQsu3Kz9 NYo

Tasks ALL: Definitions for these key terms- DNA primers, STR’s, denaturation, annealing, taq polymerase Most: Produce a flow chart to explain the stages of PCR. You should include the temperatures of each stage. Some: Why would PCR be needed when making a DNA profile/ in forensics?

Exam question Apply your knowledge to the exam question on PCR Time allowed: 10 minutes

Self-assessment