DNA Fingerprinting Flashcards
What is DNA fingerprinting?
- DNA fingerprinting is a way of telling individuals of the same
species apart - DNA sequences are variable and can therefore be used as
identifying characteristics. - DNA fingerprinting has advantages over other sources of
evidence (fingerprints, blood type, etc.): - Highly accurate.
- Can be gathered from trace crime scene evidence
What Is a DNA Fingerprint?
- Every individual carries a unique set of genes
- Chemical structure of DNA is same, but the order of the base pairs differs
- Every cell contains a complete set of DNA that identifies the organism
as a whole - Only one tenth of 1% of DNA differs from person to person
Introduction to DNA Fingerprinting and Forensics
- Forensic science – intersection of law and science
- Historic examples
- 1800s – photography
- Early 1900s – fingerprints
- DNA Fingerprinting – 1985
- Unique signature found in each person’s genetic makeup
How do you take a DNA fingerprint?
- Restriction Fragment Length Polymorphisms (RFLP)
- Restriction enzymes are molecules that can cut DNA into pieces –>
each enzyme cuts at a very specific DNA sequence - While all human beings share roughly the same DNA sequence, there
are in fact a small number of differences → these differences can be
seen by restriction enzymes
Specimen Collection- Could be a licked envelope, dirty laundry, a cigarette butt,
saliva
*Special precautions in handling specimens: gloves, disposable instruments, avoid talking
and sneezing, avoid touching sample with your skin, air-dry the evidence before packaging
so mold does not grow
*Enemies of evidence: sunlight, high temperatures, bacteria, moisture
*Ideal sample: 1 mL of fresh, whole blood (white blood cells) treated with EDTA
Agarose Gel Electrophoresis
Different banding patterns from different individuals
Summary
- Essentially, once the DNA has been cut by the enzymes,
we will have DNA fragments of various sizes - Each individual’s banding patterns should be different
because the restriction enzymes will cut each person’s
DNA at different points - Fragments of different sizes will travel different
distances along a gel when an electric current is passed
through i
Southern Blotting Methodology
Molecular technique where DNA is transferred onto a membrane
from an agarose gel and a probe is hybridized.
The first step in preparing a Southern Blot is to cut genomic DNA and run on an agarose gel.
The next step is to blot or transfer single stranded DNA
fragments on to a nylon membrane.
The next step is to hybridize a radioactively labeled DNA probe to
specific sequences on the membrane.
You will only visualize bands where the probe hybridized to the DNA
Variable Number Tandem Repeat (VNTR
*sequences that are repeated multiple times and the number of repeats varies from person to person.
- VNTRs usually occur in introns
- VNTRs can be amplified by PCR and run on agarose gels to
produce unique DNA fingerprints
Polymerase chain reaction (PCR)
PCR
Polymerase chain reaction (PCR)
* A lab technique used to amplify segments of DNA
Reaction requirements
* Template DNA – total genomic DNA isolated from anorganism that contains a target region to be amplified
* DNA primers - Short pieces of single stranded DNA that flank the target
* Taq DNA polymerase - Attaches nucleotides on the growing strand of DNA
* Nucleotides (GATC) – Polymerase
adds complementary nucleotides to the template
- Heat samples to 94°C for a minute or so to denature the
double stranded template DNA. - Drop temperature to around 50 or 60°C to allow primers to
anneal. - Maintain temperature at 72°C for a minute or two to allow
the polymerase to elongate the new DNA strands.
The thermal cycler repeats the denaturing, annealing, and
elongating temperatures approximately 30 times.
PCR amplification is logarithmic, meaning the number of
copies of the target is doubled every cycle
Applications of DNA fingerprinting
Diagnosing Disease
Genealogy
Paternity Testing
Forensics
Putting DNA to Use
- DNA fingerprinting is a comparative process
- Looking for alignment of bands or dots in the fingerprint
- All tests are based on exclusion
- Testing continues only until a difference is found
- If no difference is found after a statistically acceptable amount of testing, the probability
of a match is high
World Trade Center (9/11)
* Evident that new strategies would be necessary to quickly prepare and organize DNA profiles
and compare them with DNA profiles from relatives
* Hundreds of thousands of tissue samples from nearly 3,000 individuals
* Within 24 hours, collection points had been established around the city
* Family filed missing person reports and provided cheek cell swabs for DNA isolation; personal
items from the missing were also collected
* Several companies were involved in developing new software programs to help match DNA
samples from family members to DNA profiles of victims
* Used primarily STR, mtDNA, and SNP analysis
South Asian Tsunami
* December 2004
* Lost over 225,000 lives
* mtDNA, Y-STR’s
* Within 3 months, 800 victims had been identified
Familial Relationships and DNA Profiles
Paternity Testing
* Analyze samples from child and adults involved
Mitochondrial DNA
* Used to examine samples that cannot be analyzed by PCR or RFLP
* Older samples that lack nucleated cellular material (hair, bones, and teeth)
* Inherited from the mother only
* Changes only about 1% every million years due to random mutation
Y-Chromosome Analysis
* Passed directly from father to son
* Useful for tracing relationships among males or analyzing biological evidence
involving multiple male contributors
Nonhuman DNA Analysis
- Ginseng
- $3 million market in U.S. alone
- Two major herbal products are referred to as ginseng
- One native to North America, the other native to Asia
- Asian ginseng boosts energy; American ginseng calms nerves
- American variety is rarer and more valuable
Ancestry of Cabernet Sauvignon Grapes
* Hybrid grapes are considered inferior and are legally excluded from bearing the
prestigious dinstinction appellation d’origine contrôlée in France
* DNA evidence determined that the ancestors of cabernet sauvignon grapes are
cabernet franc and sauvignon blanc
Prove a hunter killed a bear illegally in PA
* A law makes it illegal to kill a bear in a den
* Witness reported seeing a hunter discharge gun into den
* Bear’s premolars were removed at registration station to confirm sex and age of bear
* Collected blood samples from the den and compared with DNA from bear; were a match
DNA Tagging to Fight Fraud
* Use DNA as an authentication label hidden in a wide variety of products
* Footballs in 2003 Super Bowl
* 2000 Sydney Summer Olympics
