DNA Fingerprinting

DNA Fingerprinting Applications To link a suspect to a crime scene and for criminal exonerations. O.J. Simpson and Colin Pitchfork I.D. Missing persons or Dead Person. Link a suspect to an event. Clinton – Lewinsky Scandal Paternity Cases.

DNA Fingerprinting Applications DNA fingerprinting is routinely used to test samples of blood, hair root, saliva and other bodily fluids.

DNA Fingerprinting Why is DNA an Indispensable Tool in Forensics Science? Study into the structure of the human genome has led to the discovery that portions of DNA structure of certain genes are as unique to each individual as fingerprints.

What is DNA? In 1953 James Watson & Francis Crick discovered the structure Deoxyribonucleic Acid – DNA. Double Helix Structure It is found in the nucleus of all living cells, with the exception of Red Blood Cells.

What is DNA? A person has 46 chromosomes, over 100,000 genes, 3 billion bases of DNA. Each leg of the ladder in the double helix consists of alternating sugar and phosphate units. The nucleotide bases consist of the following: Adenine (A) which pairs with Thymine (T) Cytosine (C) which pairs with Guanine (G)

What is DNA? Replication of a single strand of DNA A T A G C C A A C C A A T A T C G G T T G G T T

What is DNA? The order of the bases in a molecule of DNA provide instructions used to build proteins. A piece of DNA that contains all the information needed to build one protein is called a gene.

What is DNA Fingerprinting? In 1985 an English geneticist, Alec Jeffreys, was studying inherited variation within genes and among individuals. He studied a genetic peculiarity known as the intron. Introns are sequences of “junk” DNA that do not code for a specific protein. He noticed that some introns are made up of the same DNA base pair sequences and that the number of repetitions varies from person to person.

DNA Fingerprinting Techniques RFLP Restriction Fragment Length Polymorphisms – RFLP are the repetitive intron fragments How RFLP works: DNA from several individuals was “cut” with a restriction enzyme. The “cut” DNA is sorted by size. RFPL animation

DNA Fingerprinting Techniques RFLP (continued) Disadvantages of RFLP Advantages of RFLP Expensive. Very confident in results example: Using RFLP on a sample of blood from the O.J. Simpson murder trial said the chances someone other than Simpson left their DNA at the crime scene was 1 in 6 Billion. Time consuming. Labor intensive Requires a large sample size.

DNA Fingerprinting Techniques PCR Polymerase Chain Reaction – PCR. A technique used to “copy” DNA. Can be used with minute amounts of DNA. Uses DNA’s natural replication process to multiple sample size. PCR animation

DNA Fingerprinting Techniques PCR (continued) Disadvantages of PCR Advantages of PCR Results are not as impressive as RFLP. Small sample size needed.

DNA Fingerprinting The Power of DNA Fingerprinting Several drops of O.J. Simpson’s blood were found at the Nicole Brown-Simpson and Ronald Goldman crime scene. Both RFLP and PCR tests were performed. Here are the official results: PCR (3 Drops of Blood were tested) 1/240,000 chance blood belonged to someone other than O.J. Simpson. RFLP (2 Drops of Blood were tested) Drop #1: 1/170 Million chance blood belonged to someone other than O.J. Simpson. Drop #2: 1/57 Billion chance blood belonged to someone other than O.J. Simpson. Source: Criminalistics, An Intro to Forensics Science, Richard Saferstrein

DNA Fingerprinting A picture of DNA fingerprinting

DNA Fingerprinting Mitochondrial DNA Another structure in the cell that contains DNA is the mitochondria. Each cell contains thousands of mitochondria, each containing several Loops of DNA. Unlike nuclear DNA, this DNA is only inherited from your mother. This makes any individual with the same maternal lineage indistinguishable.

DNA Fingerprinting How DNA is used to determine Paternity DNA fingerprinting can be used to determine a child’s parents. We know you receive 50% of you nuclear DNA from mom, and the other 50% from dad.

Interpret the results of the following DNA Fingerprinting Interpret the results of the following DNA fingerprints Both daughter 1 and son 1 share genes with mom and dad, while daughter 2 has genes of mom but not the dad, and son 2 does not share genes with either parent.

CODIS is an acronym for: What is CODIS? CODIS is an acronym for: Combined DNA Index System Administered by the FBI, system which stores DNA of certain convicted felons.