Transcript DNA FINGERPRINTS - Warren Hills Regional School District

DNA FINGERPRINTS
No two people in the world have the
same DNA (except Identical twins)
• A majority of DNA is actually the same for all
humans.
• About 0.10 % variation of the human genome
(the complete genetic material in an
individual) varies from person to person.
• About 98% of our genetic makeup does
not code for any protein. This noncoding
DNA contains segments of varying lengths
with some repeating nucleotide sequences
–such as CACACA and so on.
• The number of these
repeats, and therefore
the lengths of these
segments, varies from
person to person.
A DNA fingerprint is a pattern of bands
made from specific DNA fragments of
an individual’s DNA.
DNA analysis can be used for the
following:
1) The banding patterns of the DNA fragments
from two different individuals may be compared
to establish whether they are related. (…such
as in establishing paternity).
2) DNA fingerprints of members of different
species can be compared to determine how
closely the species are related.(…such as in
evolutionary biological studies)
• DNA fingerprints can also be used for
identification of organisms in an
ecosystem, such as the salmon in a
particular stream.
3) Using DNA fingerprints to compare samples of
blood or tissue found at a crime scene with a
suspect’s blood sample may even help solve a
crime (…such as in criminology & forensics)
May 3, 2011
DNA samples from relatives
helped confirm identity yesterday
• Yesterday morning, a test that compared the dead
man’s DNA with samples collected from relatives,
confirmed that the Al Qaeda leader had been killed,
the official said on condition that he not be identified.
• Genetic material taken from siblings and other close
relatives can be used to confirm a person’s identity
because people who are related share genetic
material. Siblings, for example, share on average
half of their genes.
• Dr. Frederick Bieber, a medical geneticist
at Brigham and Women’s Hospital with
expertise in using DNA for identification,
said that such analysis is commonly used, for
example to identify people’s remains after mass
disasters, such as Hurricane Katrina.
• To do the testing, researchers extract DNA from a
sample, then use a process called polymerase chain
reaction to make many copies of specific sections of
interest. Dyes are then added to allow comparisons
of DNA fragments. Such work can be carried out
rapidly — “in a hurry, overnight, in less than 24
hours,’’ Bieber said, in laboratories that exist in most
developed countries.
• If the relative is a brother, scientists
may look at areas of the Y chromosome,
which only men have.
• If the sample comes from a sibling
who had the same mother, scientists might look at
mitochondrial DNA, which is passed on by mothers
to their children. A mathematical technique known
as a kinship analysis is used to assess the likelihood
the genetic material comes from people who are
related.
1) DNA must be extracted for analysis. (DNA may
come from people or other organisms, as well as
specimens such as blood or other tissue
residues, possibly left at crime scenes or on
victims of crimes)
2) A DNA sample may be amplified. A small
sample may be increased amount of DNA for
testing through a procedure called
polymerase chain reaction (PCR).
3) Sample DNA is cut into fragments of different
sizes by restriction enzymes.
DNA is prepared for fingerprinting
by using a process called
restriction fragment length
polymorphism (RFLP) which
cut the DNA at specific
nucleotide sequences.
The number of fragments and the length of each
fragment varies from person to person. (Specific
polymorphic regions are targeted. These regions
vary in people)
4) The fragments of DNA are then separated
using a technique called gel electrophoresis.
It separates the fragments according to size
and charge.
• DNA fragments samples are placed in wells in
the gel.
• An electric current is run through the gel. The
negatively charged DNA fragments migrate
towards the positive end of the gel.
5) DNA fragments are
split. Radioactive
probes bind to
complimentary,
single chain,
fragments of the
DNA in the samples,
forming visible
bands when exposed
to photographic film.
6) The exposed film is developed to reveal a
DNA fingerprint. The bands can then be
analyzed visually or with a computer.
The DNA fingerprinting technology compares
small segments of DNA that tend to vary the
most from person to person.
These segments are “noncoding” regions
where DNA repeats over and over again.
The photograph shows 8
columns on a gel. Several of
these columns contain DNA
fingerprints of samples
taken from a crime scene,
a victim, and four suspects.
• Which suspect’s DNA
fingerprint matches the
blood found at the crime
scene?
• How likely is it that blood
found at the crime scene
belongs to the suspect?
Virtual DNA Lab
• http://www.scq.ubc.ca/dna-restriction-digestand-gel-electrophoresis-a-virtual-lab/