Genetic fingerprinting

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  • Created by: Hindleyc
  • Created on: 20-04-19 11:55
What is GF
diagnostic tool used widely in forensic science, plant and animal breeding and medical diagnosis
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what is it based on
the fact that the DNA of every individual except identical twins in unique
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What does technique rely on the fact that
the genome of most eukaryotic organisms contains many repetitive, non-coding bases of DNA- 95% of human DNA is currently not know to code for any characteristic but may yet be found to be functional
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DNA bases which are non-coding are known as...
variable number tandem repeats VNTRs
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For every individual what does the number and length of VNTRs have
a unique pattern- they are different in all individuals except identical twins
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P of 2 individuals having identical sequences of these VNTRs is
extremely small
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however the more closely related 2 individuals are
the more similar the VNTRs will be
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What is Gel electrophoresis used for
to separate DNA fragments according to their size
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What are the DNA fragments placed on and what is applied across it
to an agar gel, voltage
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What does the resistance of the gel mean that
the larger the fragments the more slowly they move
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therefore over a fixed period the smaller fragments will
move further than the larger ones
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In this way what are DNA fragments of different lengths
separated
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If the DNA fragments are labelled eg with radioactive DNA probes what can be determined
their final position in the gel can be determined by placing a sheet of X-Ray film over the agar gel for several hours
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What expresses in the film
radioactivity from each DNA fragment and shows where the fragment is situated on the gel
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Only DNA fragments up to how many bases long can be sequenced in this way
500
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what do larger genes and whole genomes must therefore be
cut into small fragments by restriction endonucleases
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What does the making of a genetic fingerprint consist of
5 main stages- extraction, digestion, separation, hybridisation and development
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During Extraction what is even the tiniest sample of animal tissue such as a drop of blood or a hair root
enough to give a GF :)
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Whatever the sample what's the first stage
to extract the DNA by separating it from the rest of the cell
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As the amount of DNA is usually small how can its quantity be increased
using the PCR
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During digestion what happens to the DNA
then cut into fragments using the same RE
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How is the endonuclease chosen
for their ability to cut close to, but not within the target DNA
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During Separation how are the fragments of DNA next separated
according to size by gel electrophoresis under the influence of an electrical voltage
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What is the gel then immersed in
an alkali in order to separate the double strands into single strands
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During hybridisation what are used to bind with the VNTRs
radioactive (or fluorescent ) DNA probes
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what to the probes have
base sequences which are complementary to the base sequences of the VNTRs
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and what to they bind to them under
specific conditions such as temperature, ph
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What is the process carried out with
different probes which bind to different target DNA sequences
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During development what is finally done
an X-ray film is put over the nylon membrane and the film is exposed by the radiation from the radioactive probes (if using fluorescent probes positions located visually)
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because these points correspond to the positions of the DNA fragments as separated during electrophoresis what is revealed
series of bars
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What is the pattern of the bands unique to
every individual except identical twins
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summarise
E=DNA extracted from sample,D=RE's cut DNA into fragments,S=Fragments S using GE then fragments transferred from gel to nylon membrane,H=DNA probes added to label F's (Radioactive)attach to specific F,
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next
D=membrane with radioactively labelled DNA F's placed on to an Xray film,D=Development of XRAY film reveals dark bands where the radioactive DNA probes have attached
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What are DNA fingerprints from 2 samples
visually checked
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If there appears to be a match what happens
pattern of bars of each fingerprint is passed through an automated scanning machine which Calculates the length of DNA fragments from the bands
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how does it do this
using data obtained by measuring the distances travelled during electrophoresis by known lengths of DNA
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finally what is calculated
odds of someone else having an identical fingerprint
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closer the match between 2 patterns
the greater the probability that the 2 sets of DNA have come from the same person
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Uses of GF
Genetic relationships and variability, forensic science, medical diagnosis, plant and animal breeding
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What can DNA.F be used to help resolve questions of
paternity as individuals inherit half genetic material from mothers and half from fathers therefore each band on a DNA fingerprint of an individual should have a corresponding band in 1 of the parents DNA.F
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so can be used to establish whether someone is
the genetic father of a child
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What is GF also useful in determining
genetic variability within a population
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more closely 2 individuals are related
the closer the resemblance of their GF's
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populations whose members have very similar GF's has little
genetic diversity
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populations whose members have a greater variety of GF's has
a greater genetic diversity
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In forensic science where is DNA often left
at the scene of a crime eg blood hair
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What can GF establish
whether a person is likely to have been present at the crime scene although this doesn't prove they actually carried out the crime
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why
even if there is a close match between a suspects DNA and the DNA found at the crime scene it doesn't follow that the suspect carried out the crime
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other possible explanations need to be investigated such as
DNA may have been left on some other innocent occasion, DNA may belong to a V close relative, DNA sample may have been contaminated after the crime either by the suspects DNA or by chemicals that affected the action of RE used in preparing fingerprin
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Finally what has to be calculated
the probability that someone else DNA might match that of the suspect
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What is this calculation based on
the assumption that the DNA which produces a banding pattern is randomly distributed in the community
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When may this not always be the case
may not apply where religious or ethnic groups tend to have partners from within their small community
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What can genetic fingerprints help in
diagnosing diseases such as Huntington's- genetic disorder of the nervous system that results from a 3 base seq AGC at 1 end of a gene on chromosome 4 being repeated over and over again= genetic stutter
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People with fewer than 30 repeats
unlikely to get disease
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more than 38
almost certain to do so
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over 50
onset of disease will occur earlier than average
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What can a sample of DNA from person with allele for H disease be
cut with RE and DNA fingerprint prepared that can then be matched with fingerprint of people with various forms of the disease and those without the disease so in this way probability of developing symptoms and when can be determined
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What are GFs also used to
identify nature of a microbial infection by comparing the fingerprint of the microbe found in patients with that of known pathogen
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What can genetic fingerprints be used to prevent in plant and animal breeding
to prevent undesirable inbreeding during breeding programmes on farms or in zoos
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what can is also identify
plants of animals that have a particular allele of a desirable gene so individuals with this allele can be selected for breeding in order to increase the probability of their offspring having the characteristic that is produces
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Another application
determination of paternity in animals thus establishing the pedigree (family tree) of an individual
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In theory does inheritance of VNTRs have
doesn't have any influence on phenotype of an organism
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Card 2

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what is it based on

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the fact that the DNA of every individual except identical twins in unique

Card 3

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What does technique rely on the fact that

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Card 4

Front

DNA bases which are non-coding are known as...

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Card 5

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For every individual what does the number and length of VNTRs have

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