DNA fingerprinting is a method used to identify living things based on samples of their DNA. Instead of looking at the whole sequence of a person’s DNA, these techniques look at the presence or absence of common markers that can be quickly and easily identified.
1. By: Raana karimpour
DNA
FINGER PRINTING
IN GOD WE
TRUST
1Raana Karimpour
Bachelor, Department of cellular and molecular
biology, Faculty of advanced science and
technology, Tehran Medical Sciences, Islamic
Azad University, Tehran, Iran
3. DNA fingerprinting Definition
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You DNA is very special because it is what makes you, you.
Unless you have an identical twin, no one else has the same
DNA as you.This genetic identification comes from your
parents - half from mom and half from dad. But no matter how
many kids your parents have, your DNA will always be unique
from everyone else's.
DNA fingerprinting is a method used to identify living things
based on samples of their DNA. Instead of looking at the whole
sequence of a person’s DNA, these techniques look at the
presence or absence of common markers that can be quickly
and easily identified.
Raana Karimpour
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Minisatellites
• A minisatellite is a tract of repetitive DNA in which certain DNA
motifs (ranging in length from 10–60 base pairs) are typically
repeated 5-50 times. Minisatellites occur at more than 1,000
locations in the human genome and they are notable for their high
mutation rate and high diversity in the population.
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5. The Invention
• The technique was developed in 1984 by British geneticist Alec
Jeffreys, after he noticed that certain sequences of highly
variable DNA (known as minisatellites), which do not
contribute to the functions of genes, are repeated within genes.
• Jeffreys recognized that each individual has a unique pattern
of minisatellites (the only exceptions being multiple individuals
from a single zygote, such as identical twins).
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Biological Samples used for this technique
•Blood
•Hair
•Saliva
•Semen
•Body tissue cells
Cheek cell
Blood sample
Hair sample Saliva sample
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Steps to DNA Fingerprinting
DNA Isolation
PCR Amplification (Optional)
Digestion of DNA by restriction endonucleases
Gel electrophoresis
Transfer DNA on Nitrocellulose membrane
Radioactive Probe labeling
Hybridization
Autoradiography
Interpretation
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DNA isolation
• To perform DNA fingerprinting, you must first have a DNA sample! In
order to procure this, a sample containing genetic material must be
treated with different chemicals. Common sample types used today
include blood and cheek swabs.
•
• These samples must be treated with a series of chemicals to break
open cell membranes, expose the DNA sample, and remove
unwanted components – such as lipids and proteins – until relatively
pure DNA emerges.
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PCR Amplification (optional)
• If the amount of DNA in a sample is small, scientists may wish to
perform PCR – Polymerase Chain Reaction – amplification of the
sample.
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Digestion of DNA by restriction endonucleases
• The DNA is cut into fragments using Restriction Enzymes.
• Each restriction enzyme cuts DNA at a specific base sequence.
• The sections of DNA that are cut out are called restriction
fragments.
• This yields thousands of restriction fragments of all different
sizes because the base sequences being cut may be far
apart(long fragments) or close together(short fragments)
• Commonly used RE are ( Hae III, Hinf I, Alu I, etc)
• Reaction mixture incubated overnight at 37℃
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• For example, let us consider a R.E, "R" which recognizes a specific
sequence ACTTT which it cleaves between C and T. In the given
example, let us consider a double stranded DNA sequence.
GGCAACTTT....
CCGTTGAAA....
R will cut the sequence at the following site:
GGCAAC / TTT
CCGTTG / AAA
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Gel Electrophoresis
• Fragments are separated on the basis of size using a process called
Gel electrophoresis
• DNA fragments are injected into wells and an electric current is
applied along the gel.
• DNA is negatively charged so it is attracted to the positive end of the
gel.
• The shorter DNA fragments move faster than the longer fragments
• DNA is separated on basis of size.
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Transfer DNA on Nitrocellulose membrane
• The DNA fragments are transferred to a Nylon sheet by placing the
sheet on the gel and soaking them overnight by the process southern
blot.
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Radioactive Probe labeling
• Adding radioactive or colored probes to the Nylon sheet which is
complementary to target sequence.
• Each probe only sticks to one or two specific places on the sheet.
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Hybridization
• Labeled probe DNA should be hybridized with the complementary
sequences located on nylon membrane for the detection of position
of later.
• Membrane is washed to remove non specific binding and clearing of
the background.
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Autoradiography
• To detect the sequence in genome bound with the hybridized
radioactive probe on membrane.
• Technique involves alignment of hybridized membrane with X-ray
film.
• The X-ray film alter its development shows multiple no. of band s
that looks like barcodes and knowns as DNA fingerprints.
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Interpretation of band patterns
• Analysis of band patterns of different individuals.
• Comparison of position of bands
• Computer software are also available for the analysis of DNA
fingerprints.
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Modifications of the method
• Types of repeats used in DNA profiling include Variable Number
Tandem Repeats (VNTRs), especially short tandem repeats (STRs),
which are also referred to by scientists as “microsatellites” or
“minisatellites.”
• Different DNA fingerprinting methods exist, using either restriction
fragment length polymorphism (RFLP), polymerase chain reaction
(PCR), or both. Each method targets different repeating polymorphic
regions of DNA, including single nucleotide polymorphisms (SNPs)
and short tandem repeats (STRs). The odds of identifying an
individual correctly depend on the number of repeating sequences
tested and their size.
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DNA Profiling
• Modern-day DNA profiling is also called STR analysis and relies on
microsatellites rather than the minisatellites used in DNA
fingerprinting.
• STRs (Short Tandem Repeats) and SSRs (Simple Sequence
Repeats) are 2-6 base pair long repeating sequences. These are
unique for every individual and are shorter than VNTRs. Hence they
produce accurate DNA fingerprints
• Microsatellites, or short tandem repeats (STRs), are the shorter
relatives of minisatellites usually two to five base pairs long. Like
minisatellites they are repeated many times throughout the human
genome, for example ‘TATATATATATA’.
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DNA Fingerprinting Usages
Biological evidence
Wildlife forensics
Establishment of paternity
Person identification
Diagnosis of inherited disorders
Developing cures for inherited disorders
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Wildlife Forensics
• As most TV watchers know, DNA fingerprinting can be accomplished
with a very small quantity of DNA and is a sure-fire way to "finger" a
culprit in a crime. Similarly, DNA fingerprinting can and does
exonerate innocent people of crimes—sometimes even crimes
committed years ago. DNA fingerprinting also can be easily used to
identify a decomposing body.
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Illustration showing a comparison of a DNA fingerprint from a crime
scene and DNA fingerprints from two suspects.The DNA fingerprint
from suspect 2 matches that taken from the crime scene.
Image credit: Genome Research Limited
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•It was first used as evidence in 1987, when baker Colin
Pitchfork was the first criminal caught using DNA
fingerprinting in Leicester. It was also used to clear the
original suspect Richard Buckland.
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Diagnosis of inherited disorders
• Helps diagnose disorders in both prenatal and newborn babies.
• Disorders may include cystic fibrosis, hemophilia, Huntington’s
disease, familial Alzheimer's , sickle cell anemia, thalassemia and
much more.
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Non criminal identification
• Is Joe really Billy's father? DNA fingerprinting can answer that
question quickly and accurately. In addition to identifying adoptive
children and settling paternity suits, DNA fingerprinting also has
been used to establish a relationship in the case of inheritance. More
than once, DNA fingerprinting has made it possible for people
separated as a result of natural disaster or war to find their children
and parents.
• This information can be used
• in:
Paternity suits
Inheritance cases
Immigration cases
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Illustration comparing the DNA profiles of two parents and
their child.You can see which STRs in the child have been
inherited from which parent.
Image credit:Genome Research Limited
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Uses of DNA Fingerprinting
Personal identification
The U.S. armed services are just beginning a program where
they collect DNA fingerprints from all personnel for later use, in
case they need to identify casualties or missing people.
Also, The UK NDAD a national DNA Database set up in 1995. At
the end of 2005, it carried the profiles of around 3.1 million
people, over 585,000 of them taken from children aged under
16. At the end of 2006, this figure had risen to more than four
million records, making it the world's biggest DNA database at
the time.
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Famous Cases
• One of the most famous historical cases impacted by DNA
fingerprinting was the murder of Czar Nicholas II and his family
following the Russian Revolution in 1917. According
to Smithsonian magazine, remains found in 1979 ultimately
underwent DNA testing and were confirmed to be members of the
czar's family.
• Colin Pitchfork was the first criminal caught based on DNA
fingerprinting evidence.
• He was arrested 1986 for the rape and murder of two girls and was
sentenced in 1988.
• O.J. Simpson was cleared of a double murder charge in 1994 which
relied heavily on DNA evidence.
• This case highlighted lab difficulties.
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References
o Molecular Diagnostic Applications in Forensic Science H.E.
McKiernan and P.B. Danielson
o DNA Fingerprinting: An Introduction by Lorne T. Kirby,
Macmillan/Srockton Press (Breakthrough in Molecular Biology
Series), 1990.
o Forensic application of DNA “Fingerprints”, Peter Gill, Alec J.
Jeffreys & David J. Werrett
o The Similarity Index and DNA Fingerprinting’ Michael Lynch
o A PCR-based DNA fingerprinting technique: AFLP for molecular
typing of bacteria Jhy-Jhu Lin, Jonathan Kuo and Jin Ma
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