DNA Fingerprinting

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DNA Fingerprinting
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Content

• The structure of DNA
• History of DNA fingerprinting
• DNA Electrophoresis
• DNA fingerprinting application

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The structure of DNA

• The characteristics of all living organisms,
  including humans, are essentially determined by
  information contained within DNA that they
  inherit from their parents. The molecular
  structure of DNA can be imagined as a zipper with
  each tooth represented by one of four letters (A,
  C, G, or T), and with opposite teeth forming one
  of two pairs, either A-T or G-C.

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• The letters A, C, G, and T stand for adenine,
  cytosine, guanine, and thymine, the basic
  building blocks of DNA.
• The information contained in DNA is determined
  primarily by the sequence of letters along the
  zipper. For example, the sequence ACGCT
  represents different information than the
  sequence AGTCC in the same way that the word
  "POST" has a different meaning from "STOP" or
  "POTS," even though they use the same letters.
  The traits of a human being are the result of
  information contained in the DNA code.

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• Living organisms that look different or have
  different characteristics also have different DNA
  sequences. The more varied the organisms, the
  more varied the DNA sequences. DNA fingerprinting
  is a very quick way to compare the DNA sequences
  of any two living organisms.

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History

• DNA fingerprinting was developed in 1984 by Alec.
  J. Jeffrey at the University of Leicester while
  he was studying the gene for myoglobin
• He found that myoglobin genes contain many
  segments that vary in size and composition and
  have no apparent functions

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• Jeffrey called these segments minisatellites
  because they were small and surrounding the part
  of the gene.
• In 1987, British baker Colin Pitchfork was the
  first criminal caught using DNA fingerprinting
• 1990 California establishes DNA fingerprint banks
  for sex offenders.

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DNA Electrophoresis Experiment

• Electrophoresis is a technique that can be used
  to separate the DNA and RNA fragments from one
  another according to their sizes.

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• It can be done by loading the fragments(??) in a
  well at one end of a piece of gel,which is
  immersed in a buffer solution inside a gel tray.
• An electrical current is then passed through the
  gel.

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Diagram showing gel electrophoresis
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• As DNA or RNA molecules contain many phosphate
  groups,they are highly negatively charged.The
  fragments are attracted towards the positively
  charged electrode.
• The fragements pass through a gel at a rate that
  is inversely proportional to their size.Small
  fragments move faster than large fragments
  through the gel.In other words,they travel
  further through the gel.This procedure can be
  used to separate different DNA or RNA fragments
  into bands

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• These bands can be visualized by staining the gel
  with ethidium bromide.It is a dye that
  intercalates between the nitrogenous bases and
  gives a pinkish orange colour under UV
  light.Usually a marker is loaded together with
  the sample that contains bands with known
  sizes.In this way,the sizes of unknown fragments
  can be estimated.

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• The DNA sequences of DNA fragments can be known
  by means of an automated DNA sequencing machine.

DNA sequencing result
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Home Made Gel for Electrophoresis
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Procedure of DNA fingerprinting

• 1 Isolation of DNA.DNA must be recovered from
  the cells or tissues of the body. Only a small
  amount of tissue - like blood, hair, or skin - is
  needed. For example, the amount of DNA found at
  the root of one hair is usually sufficient.
• 2 Cutting, sizing, and sorting.Special enzymes
  called restriction enzymes are used to cut the
  DNA at specific places. For example, an enzyme
  called EcoR1, found in bacteria, will cut DNA
  only when the sequence GAATTC occurs. The DNA
  pieces are sorted according to size by a sieving
  technique called electrophoresis. The DNA pieces
  are passed through a gel made from seaweed
  agarose (a jelly-like product made from seaweed).
  This technique is the biotechnology equivalent of
  screening sand through progressively finer mesh
  screens to determine particle sizes.

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• 3 Transfer of DNA to nylon.The distribution of
  DNA pieces is transferred to a nylon sheet by
  placing the sheet on the gel and soaking them
  overnight.
• 4-5 Probing.Adding radioactive or colored
  probes to the nylon sheet produces a pattern
  called the DNA fingerprint. Each probe typically
  sticks in only one or two specific places on the
  nylon sheet.

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• 6 DNA fingerprint.The final DNA
  fingerprint is built by using several probes
  (5-10 or more) simultaneously. It resembles the
  bar codes used by grocery store scanners

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DNA fingerprinting application

• parentage test
• Forensic science
• DNA ID Card

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Uses in parentage test

• DNA fingerprinting is widely used in parentage
  testing around the world. By comparing different
  DNA sequences, we can analyse the relationship
  between any two individuals.

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• The test will be conducted using the latest in
  PCR (Polymerase Chain Reaction) technology. The
  PCR method is the most widely used and trusted
  DNA testing technology today.

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• Polymerase chain reaction (PCR) is a molecular
  biology technique for enzymatically replicating
  DNA without using a living organism. Like
  amplification using living organisms, the
  technique allows a small amount of the DNA
  molecule to be amplified exponentially.

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• The results that you receive will look like a
  table full of numbers. There are three columns
  one for the Mother, one for the Child and one for
  the possible Father. Each row in the table
  represents a different DNA locus, which represent
  that specific area on their individual DNA .

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Uses in forensics

• Because human DNA is unique to individuals, DNA
  isolated from blood, hair, skin cell, or other
  genetic evidence left at the scene of crime can
  be compared, using the DNA fingerprinting
  technology, with the DNA of a criminal suspect to
  determine guilt or innocence.

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• In criminal cases, this generally involves
  obtaining samples from crime-scene evidence and a
  suspect, extracting the DNA, and analyzing it for
  the presence of a set of specific DNA regions
  (markers).

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• Scientists find the markers in a DNA sample by
  designing small pieces of DNA (probes) that will
  each seek out and bind to a complementary DNA
  sequence in the sample.

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• Forensic scientists compare these DNA profiles to
  determine whether the suspect's sample matches
  the evidence sample. If the sample profiles don't
  match, the person did not contribute the DNA at
  the crime scene.

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DNA ID Card

• The DNA ID Card contains your personal
  information and DNA profile. The information
  recorded on the card includes photograph, Name,
  Gender, Date of Birth and DNA personal profile.