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)

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.

May 3, 2011

• 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-digest-and-gel-electrophoresis-a-virtual-lab/