Discovered in 1984 by Dr. Alec Jeffreys at the university of Leicester

Was knighted for his discovery

What do you know about DNA Profiling? How does it work? From what sources can DNA for profiling be

obtained? How reliable is it? How is enough DNA obtained when little is

available from the crime scene? What, exactly, is a DNA profile or fingerprint?

Take 5 minutes with your lab partner and discuss these questions

Identification of remains

Josef Mengele was a Nazi war criminal notorious for grotesque human experiments that he carried out at the Auschwitz concentration camp.

After the Second World War he fled from the Allies and escaped to South America. The fugitive succeeded in living out the rest of his days without being caught.

In 1985 investigators went to the cemetery of Nossa Senhora do Rosario in the small Brazilian town of Embu to dig up the skeleton of a man who had been drowned in a swimming accident six years previously.

Using DNA extracted from blood provided by Mengele’s wife and son, it was concluded that it was more than 99.94% certain that the skeleton was Mengele’s.

Who’s your daddy?

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Kirk Bloodsworth Convicted in 1985 for

the rape and strangulation of a 9-year old girl and sent to death row

In 1992, defense attorneys were successful in having a dime-sized semen stain on the girl’s underpants tested against Bloodsworth’s DNA

He was exonerated

“I didn’t understand the DNA stuff at all. To me, it was just a waste of time. It was way out there and carried absolutely no weight with me at all.”

Post-trial commentary from a juror in the O.J. Simpson trial: V. Bugliosi, Outrage (New York: Dell Publishing, 1996).

“In a forensic setting, ... an innocent suspect has little to fear from DNA evidence, unless he or she has an evil twin.”

N. Risch & B. Devlin, “On the Probability of Matching DNA Fingerprints” (1992) 255 Science.

DNA Analysis is useful because: The DNA contains “detectable” patterns unique to each

individual DNA is a robust molecule, and is stable under most (but

not all) environmental conditions DNA can be isolated from a wide range of biological

samples likely present at a crime scene The source of DNA doesn’t matter – it is the same in all

sources (blood, semen, sputum, skin etc) Rapid advances in technology allow the precise

patterns to be detected even with very small samples (a blood spot, single hair follicle, lip-prints on a glass, physical fingerprints, saliva/skin on a cigarette butt etc)

Methods are fast and relatively cheap Data are complied in databases, and are easily

searched

Blood (White blood cells) Semen (Sperm cells) Hair with roots (Hair follicle cells) Skin, dandruff (Skin cells) Sweat stains (Skin cells sloughed

off) Vaginal fluids (Mucosal surfaces) Nasal secretions (Mucosal surfaces) Urine (Mucosal surfaces) Feces (Digestive system

cells)

Biology 101: Every cell in your body contains the same set

of DNA (except sperm/eggs) DNA is unique to each individual: even though

we share 99.9% of our genome in common with other humans, 0.1% of 3 billion nucleotides is a significant and detectable level of difference (1 out of every 1000 nucleotides)

Most variation exists in non-coding (viz. “junk DNA”) regions.

Mutations in the non-coding are tolerated and can accumulate with no effect on the organism

The challenge: find the differences!

Restriction Fragment Length Polymorphisms (RFLPs) Restriction from the enzymes that cut the DNA

(restriction enzymes) Fragment for the fragments produced by the cutting Length and Polymorphisms for the different sized

fragments produced (polymorphic = many forms)

DNA is cut by molecular “scissors” – enzymes which recognize particular sequences of nucleotides

These enzymes identify short sequences of DNA, then snip it

Because everyone’s DNA is different, enzymes cut in different places

The resulting samples contain DNA fragments of different size (Restriction Fragment Length Polymorphisms)

DNA is visualized using electrophoresis Negatively charged DNA moves through a gel

with a current Smaller DNA moves faster than larger DNA

fragments

The probability of 2 people having exactly the same DNA profile is between

1 in 5 million to1 in 100 billion

(greater than the population of humans on earth)

This number becomes even larger if you consider more regions of DNA

Thus, the odds that the DNA evidence from a crime scene will match your DNA profile is astronomically small (unless you have an evil identical twin)

Although DNA is relatively stable, it does denature or get destroyed through enzyme action, from bacteria or through oxidation

Therefore, samples should be collected soon and preserved (usually in a buffer and by freezing) if possible

Care should also be taken not to cross contaminate during collection

Blood is also a potential pathogen, so care must be taken to avoid exposing yourself to blood borne viruses like Hep B, tuberculosis or HIV

1. Break open the cells Mortar pestle Lysis buffer Centrifugation Micro pestles

This is important for 2 reasons: It is a standard or control (i.e.

important for Daubert challenges) – one needs to argue that the same amount of DNA is used in each lab, by each lab technician and every time sample is processed

The amount has been optimized for subsequent reactions – so it ensures optimal results

Quantification is done by some form of fluorescence – tagging DNA with a fluorescent tag, and the more DNA there is, the brighter it will be

Because most tissue samples from a crime scene contain very little DNA, the goal is amplify, or make many copies of the DNA of interest

In STR analysis, you want to amplify the DNA containing the tandem repeats and only this DNA

The process used is called Polymerase Chain Reaction (PCR)

PCR Machines, or thermocyclers, use repeated cycles of heat and cooling to replicate the DNA using many of the same enzymes found in cells which facilitate DNA replication

How to amplify DNA...

CODIS – Combined DNA Index System

Uses 13 loci Terameric repeats All forensic laboratories that use the CODIS

system can contribute to a national database. Only Mississippi doesn’t participate The Forensic Index contains DNA profiles from

crime scene evidence. The Offender Index contains DNA profiles of

individuals convicted of sex offenses (and other violent crimes) with many states now expanding legislation to include other felonies. Forensic Profiles in NDIS: 119,782 Convicted Offender Profiles in NDIS: 2,643,409

By combining the frequency information for all 13 CODIS loci, the frequency of this profile would be 1 in 7.7 quadrillion Caucasians

Two teenage girls raped and murdered in Leicestershire, England

Semen from the victims indicated a male with Type A blood and a rare enzyme = 10% of the local male population

A local boy, Richard Buckland, confesses upon interrogation

Police use DNA fingerprinting to confirm, but DNA profiles of Buckland and crime scene DNA do not match

Ironically, Buckland becomes the first person exonerated by DNA evidence

Police request DNA samples from all adult males in 3 nearby villages (5000 men)

6 months later – no results! A year later, police are informed by a

bakery worker that they overheard a co-worker bragging they had given a DNA sample for another man

Police obtain DNA from Colin Pitchfork and obtain a perfect match

In 1988, Colin Pitchfork was tried and convicted and sentenced to life in prison for the double rape and homicide based in large part to the DNA evidence

A physician in Canada eludes authorities for years Accused of drugging and sexually assaulting

patients, DNA profiles from semen samples from the assaulted women do not match Dr. Schneeberger

Blood was drawn on 3 occasions in 1992, 1993 and 1996, but never came back as a match

Finally police obtain blood from a finger prick, swabbed the inside of his cheek and took hair samples

The results matched the DNA from the semen of the victims

How did he get away with it?

On the previous 3 occasions, blood was drawn from the same arm

The last time the blood was drawn, the technician stated that the blood looked brown and “old”

Schneeberger had surgically implanted a piece of rubber tubing in his arm and filled it with stored blood from a patient

Recall from general biology the heirarchy of structure of DNA:

Humans carry 2 copies of the DNA in their cells (diploid). The exception is sperm and eggs which contain one copy (haploid)

The DNA is organized into chromosomes – long strands of DNA On the chromosomes, genes (sequences of DNA that code for

a protein) are found. The location of the gene on the chromosome is its locus (plural: loci).

Much of the DNA is non-coding (junk DNA) and even in protein coding genes, there may be sequences that are cut out (introns) before they are used to make a protein. The remaining sequences are the exons.

Genes are sequences of DNA – there are only 4 building blocks of DNA (A,T,G and C), so the genes are actually sequences of these nucleotides. The length and order of nucleotides determines the type of protein that is produced by that gene.

Differences exist between individuals largely in the non-coding DNA (introns and junk DNA). DNA profiles detect and exploit these differences