forensics lecture 5 - DNA profiling 2 Flashcards
what are the methods of DNA profiling?
-RFLP (Restriction Fragment Length Polymorphisms)
-PCR amplifies STRs or SNPs (Short tandem repeats/Single nucleotide polymorphisms)
-Low Copy Number analysis
-Y-STR testing
-Mitochondrial DNA
-DNA Boost
what are the applications of DNA profiling?
-Familial searching
-Cold Cases
-Linking/identifying families
-Wildlife crime
-Ethical issues
what is the probability of a DNA profile match?
-DNA identification based on probabilities
-Using 13 CODIS sites = 1 in ten trillion
-World population 7.5 billion
type of conclusions = Exclusion (non-match), Inclusion (match), Inconclusive
how do you find the probability of alleles?
For a two-allele locus
frequency of allele 1, f(1) = p
frequency of allele 2, f(2) = q
p + q = 1
If homozygous for f(1,1) = f(1) x f(1) = p x p = p2
If homozygous for f(2, 2) = f(2) x f(2) = q x q = q2
If heterozygous, f(1, 2) = 2(pq)
how would you find the answer to this equation?
What is the likelihood that an individual at random would have the same pattern of a 5 and 7 repeat for the THO1 STR?
with the THO1 being 1/200 and 1/6
you would do 2 x 1/200 and 1/6
so 2/1 x 1/200 x 1/6 = 2/1200 = 1/600
what are the sources of error for this?
-Degraded DNA
-Human Error
-Technical Failure
-Contamination
-PCR stutter in STR analysis
what is the analysis of low copy number DNA?
-LCN – Low copy number
-Same discriminatory power as routine DNA profiling
-Copy 10 informative sites (STR regions) from smaller amount of starting material
-Takes longer to process
what is partial profiles used for?
-Used for familial searching
-Prioritise using specific parameters (location and police intelligence)
-Can use low copy number profiling
how has DNA technology helped in cold cases
Advances in DNA technology has led to an increase in examination of “Cold cases”
DNA boost October 2006
(Computer-based analysis system to interpret mixtures)
what was the shoe rapist example?
-1980s women in Rotherham & Barnsley tied up with tights, raped & shoes stolen
-Case re-opened in 2001
-Familial searching – 40 close matches
-Sister of James Lloyd – sample had been taken on arrest for drink-driving
-Lloyd admitted raping 4 women & attempted rape of 2 others
what was the example of the Romanovs?
Tsar Nicholas II, his wife & 5 children executed 1918
Grave located in 1991
STR analyses & mt DNA analyses indicated 5 of 9 skeletons in a grave were of the same family
mtDNA was compared with living direct relatives
Prince Philip – son of daughter of tsarina’s sister – unbroken female lineage
Tsar confirmed from mt DNA of his brother
Woman, who claimed to be Anastasia – mt DNA different
how does DNA profiling aid in genetic diseases?
-Mutations in genes can lead to defects
-Genetic diversity – polymorphism
-Mutations within restriction sites changes the sizes of fragments
-Detect genetic diseases by RFLP or PCR
e.g. Sickle-cell anaemia, cystic fibrosis
-Current standard Forensic DNA tests do not look at genes
what are the non-human applications of DNA profiling?
-Trade in wildlife
-Threat to species
-Non-human DNA – crimes against people/property
-Conservation & breeding management
-Evolutionary analysis
what are the ethical problems with DNA profiling?
Should we all have our DNA profiles on a central database?
Would this make most crimes solvable?
Would it result in unfair convictions or framing?
Is it an invasion of privacy?
what is familial searching? and an example
If you have a Full DNA profile but no matches on DNA database
Look for similar DNA profiles suggesting family group on the database
Alternatively – may have partial profile – try to match
M3 murder=
March 2003 Craig Harman & friend tried to steal a Renault Clio
Bricks were thrown onto traffic in a footbridge over the M3
Mixed profile from brick matched full profile from Clio (using LCN)
No match
Ethnic markers – white male
Familial search – white males under 35
16 of 20 matches – close relative of suspect
Led to Craig Harman – DNA sample matched
