DNA

Charlotte Camilla
Flashcards by Charlotte Camilla, updated more than 1 year ago
Charlotte Camilla
Created by Charlotte Camilla about 7 years ago
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Flashcards on DNA and the DNA database based on semester 2 of SIC at UWE.

Resource summary

Question Answer
What are the typical biological samples collected for DNA? Blood Semen Saliva Skin Hair
What was the first murder case solved by DNA? The murders of Lynda Mann (1983) and Dawn Ashworth (1986). Richard Buckland was the main suspect in the cases as he knew information about the cases that was not made public and he confessed to one of the murders. The blood group and ezyme typing that was obtained matched 10% of the population including the suspect. Alec Jeffreys who discovered the technique for genetic profiling, compared the DNA profile of Buckland to scene was not a match so he could not have committed either murders. A mass screening on three nearby villages was performed and Colin Pitchfork was identifed and convicted in 1988.
What were the phases of DNA technology? Phase 1: 1987 - RFLP MLPs (Restriction fragment length polymorphism multi locus probes). Phase 2: 1989 SLP (single locus probes). Phase 3: 1991 PCR (Polymerase Chain Reaction) with SLP Phase 4: 1994 STR (Short Tandem Repeats) Phase 5: April 1995 Launch of the DNA database. Phase 6: 1999 FSS SGM-PlusTM system that uses 10 loci markers. Probability of a match at random taken to be less than 1 in a billion (1 in 109). Phase 7: 1999 LCN (Low Copy Number) – now called Low Template (LT) DNA. This is a particular technique for working with the smallest sample – a single cell. Mitochondrial DNA: obviously much less discriminating but has uses when only old bones or hair shafts are available.
Potentials and Limitations for RFLP MLPs? The can create a highly individual pattern - if the sample is of good quality, high quantity and from a single source. Could isolate sperm from vaginal fluids Difficult for blood as it required a stain size of 50p piece – ideal for rape cases. It was impossible to obtain a pattern when analysing a mixed sample. There was limited statistcs for the profiles. Was an extremely slow process, took 6-8 weeks for analysis. Was prone to band shifting and contamination between lanes.
Single locus probes Single locus probes were more sensitive than RFLP MLPs and made it possible to analyse mixed samples. Was much quicker, 1 probe only took a few days, four probes took between 1-2 weeks. A statistical database was developed and single locus probes made it possible to work with small stains.
PCR with SLP Made it possible to obtain a profile from a smaller sample e.g. 20 head hairs (with root). Only 0.1-1ng of DNA was required compared with 50-500ng DNA for original RFLP method.
STR – Short Tandem Repeats Analysed four loci simultaneously and was the first multi complex system. The technique is automated and involves applying fluorescent labels to the DNA, analysing them with laser readers and digitally storing the results.
Short tandem repeats sections of DNA with repeating bases i.e. GACGACGACGACGACGAC
What is the probablity of matching the profile of a full sibling? 1 in 10 000.
How does the nDNA database work? The database contains subject sample profiles taken from known individuals and crime scene sample profiles. Crime scene sample profiles are compared with each other to establish links between different scenes. Crime scene profiles are also compared to suspect sample profiles to ID suspects. There is a 60% probability of a Crime Scene profile matching a Suspect Sample. In other words there is a 60% probability of IDing a suspect. 80% of the matches are related to offences other than initial arrest offence.
In the UK can you be convicted solely on the basis of DNA evidence? NO - No-one can be convicted in this country on the basis of DNA evidence alone. It is not PROOF of identity (in UK).
What is ALFIE? Allele Frequency for Inference of Ethnicity Certain alleles (lengths of fragments at particular loci) are more common in particular ethnic groupings. This is used in the investigative stages and is not evidentiary.
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