DNA Fingerprinting DNA Profiling

Purposes: Determine Identity (match tissue samples) Establish Paternity

DNA as Forensic Evidence Individual evidence – identify a single person Trace evidence – small amount left at crime scene Found in saliva, blood, semen, skin, hair roots, urine (nuclear DNA) Hair, bones, teeth (mtDNA)

Collection of DNA Avoid contamination Preserve carefully Wear gloves, avoid sneezing or coughing Preserve carefully Air-dry samples If wet, store in freezer

Basic DNA Facts: Stores genetic information Tightly coiled to form chromosomes deoxyribonucleic acid 4 nitrogen bases: A (adenine), G (guanine), C (cytosine), T (thymine) Double-stranded Structure discovered by Watson and Crick

Basic DNA Facts: Found in nucleus of cells Approx. 3 billion base pairs Exons: encoded DNA <1.5% of DNA Introns: uncoded DNA (“junk” DNA?) > 98.5% of DNA Mitochondrial DNA (mtDNA): inherited only from mother Only identical twins have identical DNA

Chromosomes Each person has 46 chromosomes 23 pairs – 1 set from mom, 1 set from dad Genes: segment of DNA that contains info to produce a protein Allele: alternate forms of a gene Inherit 1 allele from mom, 1 allele from dad

Examine an individual’s DNA sequence to develop a DNA fingerprint DNA Profiling: Examine an individual’s DNA sequence to develop a DNA fingerprint

Steps of DNA Fingerprinting Extraction: take DNA out of cells Amplification: make copies of DNA Use PCR (polymerase chain reaction) Electrophoresis: DNA pieces separated within an agarose gel or capillary tube Visible bands of DNA form a unique pattern Pattern = “fingerprint”

PCR Machine: Amplifies (makes copies of) DNA

Gel Electrophoresis

DNA Fingerprint (using gel electrophoresis)

DNA TESTING 99.9% of DNA shared by humans Polymorphisms: differences in DNA sequences (0.1%) RFLP Analysis – older method, requires quarter-sized DNA samples STR (short tandem repeat) Within noncoding DNA regions (loci), 2-5 bases in length repeated Very small or degraded DNA samples Examine 13 regions (loci) for forensic analysis Most current technology in use!

Capillary Electrophoresis (CE)

DNA Profile

Crime Scene Matching (To establish identity – all bands must match)

Paternity A child inherits 1 set of genes from mom, 1 set from dad ½ of the bands in a pattern are from mom; the other ½ from dad

Lab 15: Who did it?

Lab 15: Who did it?

Lab 15: Who did it?

mtDNA – trace maternal relatives Evidence: hair, old bones/teeth Famous case: Anna Anderson = Anastasia Romanov (Russian princess)? No Y-STR – trace paternal relatives Y-chromosome analysis Famous case: Did Thomas Jefferson father children with his slave, Sally Hemmings? Blood taken from descendents of Jefferson’s uncle & Hemming’s sons Yes

CODIS Combined DNA Index System Electronic database of DNA profiles Fully operational since 1998 Profile = 13 loci from STR analysis 1 in a Quadrillion possibility of a match As of February 2011: 9.4 million offender profiles (DNA from convicted felons of violent crimes) 360,000 forensic profiles (DNA from crime scenes) 138,700 hits made

CODIS (continued) STR Profiles entered into CODIS: Convicted offender Forensic (crime scene DNA) Arrestees Unidentified human remains Biological relatives of missing persons Future of CODIS: mtDNA (degraded samples, hair, bones, teeth) Y-STR (sexual assault) miniSTR (highly degraded samples)

Uses of DNA in Forensic Identification Identifying September 11th victims DNA Shoah Project: genetic database of people who lost family during the Holocaust Disappeared children in Argentina (1970’s) Tomb of the Unknowns (Arlington National Cemetery) Remains of Romanov family (last Russian Czar) Evolution of human migration patterns