DNA AnalysisDNA Analysis

What is DNA?What is DNA?Deoxyribonucleic AcidGenes found on a chromosome

are composed of DNADNA contains all of our body’s

genetic material

DNA StructureDNA StructureComposed of a sugar, phosphate

group and a nitrogen base

Sugar: DeoxyribosePhosphate group: Phosphate ionNitrogenous bases: Adenine,

Guanine, Cytosine, Thymine

Complimentary Base Complimentary Base PairingPairingAdenine with ThymineGuanine with Cytosine

Major Sources of DNAMajor Sources of DNABloodSalivaHair with a rootSemenSkin

Collecting DNACollecting DNA1. Wear disposable gloves2. Use disposable instruments for

each sample3. Avoid touching the area where

DNA may be found4. Avoid talking, sneezing and

coughing over evidence (mask)5. Avoid touching your face, nose

and mouth when collecting evidence

Collecting DNACollecting DNA6. Air-dry evidence thoroughly

before packaging7. Put evidence into new paper

bags or envelopes8. If wet evidence cannot be

dried, it may be frozen

Mitochondrial DNAMitochondrial DNADNA found only in the

mitochondria of the cellInherited from the MOTHER ONLY

Mitochondria DNAMitochondria DNAAdvantages

◦More sensitive than nuclear DNA (less needed for testing)

◦Degrades slower than nuclear DNA◦Can be used in cases where nuclear

DNA cannot (hair w/o root, skeletal remains)

Mitochondrial DNAMitochondrial DNADisadvantages

◦All people of the same maternal line will be indistinguishable

◦More work, more time consuming, more costly

Junk DNAJunk DNA95% of your genetic code doesn’t

code for any proteinThis means that only 5% creates

the proteins (genes) that make you, YOU!

Variable Number Tandem Variable Number Tandem Repeats (VNTR’s)Repeats (VNTR’s)Short identical repeat sequences

of DNAA particular sequence that you

want to be copied can be repeated up to 30 times

Used so you can test multiple times

Short Tandem Repeats Short Tandem Repeats (STR’s)(STR’s)Repeats of 2-7 bases with a total

length of 100-400 base pairsThey are shorter so they are less

susceptible to breakageLoci of choice for laboratory

analysisIdeal size for PCR (Polymerase

Chain Reaction)

FBI Standard Reference FBI Standard Reference LociLoci

DNA FingerprintingDNA FingerprintingUsed to identify individuals by

their STR regions

Steps to creating a DNA Steps to creating a DNA fingerprintfingerprint1. Isolate the DNA 2. Cut the DNA at a specific site

using a restriction enzyme to create short DNA fragments

3. Use PCR to amplify the fragments

4. Sort the fragments according to size using gel electrophoresis

Steps Cont.Steps Cont.5. Use a radioactive probe to

label the VNTR’s that you wish to look at

6. Use x-ray film to take a picture or view you gel over a light source

Restriction Fragment Length Restriction Fragment Length Polymorphism (RFLP’s)Polymorphism (RFLP’s)Occurs when the genetic length

of a specific fragment varies between individuals

Polymerase Chain Reaction Polymerase Chain Reaction (PCR)(PCR)Devised in 1983 to amplify small

amounts of DNACan be performed using the DNA

from 1 cellThe amplified DNA can then be

used to: - Identify a suspect or victim, determine sex, determine species

PCR TechniquePCR Technique

CODISCODISCombined DNA Index SystemNational software developed by

the FBIDistributed to local, state and

national crime labsAll 50 states mandate inclusion

of DNA fingerprints from all violent criminals and sex offenders

CODISCODISUses 13 STR regionsThousands of matches have led

to the capture of criminals that otherwise would never have been caught

It has also led to the exoneration of many criminals wrongfully imprisoned