DNA Profiling LO: 5 Describe how DNA profiling is used for identification and determining genetic relationships between organisms (plants and animals). 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 it. 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 STR’s: 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 STR’s 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 STR’s. Enzymes are optimum for this. Specifically restriction enzymes (restriction endonucleases) which cuts at specified 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, arrested in 1986 for the rape and murder of two girls. He was only caught in 1987 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. 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.