DNA Profiling(DNA fingerprinting)
http://www.pbs.org/wgbh/nova/sheppard/cleared.html
What is DNA Profiling? A technique used by scientists to distinguishbetween individuals of the same species usingonly samples of their DNA. Invented in 1985.
Stages of DNA Profiling
• Stage 1: Cells are broken down to release DNA (DNA extraction)
If only a small amount of DNA is available it can beamplified using thepolymerase chain reaction(PCR)
Stages of DNA Profiling • Step 2: The DNA is cut into fragments using different restrictionenzymes.
Each restriction enzyme cuts DNA at a specific base sequence.
The sections of DNA that are cut out are called restriction fragments.
Stages of DNA Profiling
This yields many restriction fragments of all differentsizes because the base sequences being cut may be farapart (long fragment) or close together (short
fragment).
Restriction enzymes can cut at coding regions(genes which code for proteins) or non-coding regions
About 99.5% of our DNA is the same –at the coding regions (if different= mutation). We differ in our non-coding regions.
VNTRsIn non-coding regions, variations in variablenumber tandem repeats (VNTRs) may exist.This will produce different # of fragments whenDNA is cut with restrictions enzymes.
Imagine DNA cut with restriction enzyme that recognized CC↓GG
Person #1AATATACCGGATATTTTATATTTTATATTTTCCGGTT
Person #2AATATACCGGATATTTTATATTTTCCGGTTACCGGTT
Fragments generated by Person #1 Fragments generated by Person #2
8 bp, 25 bp, 4 bp 8 bp, 18 bp, 7 bp, 4 bp
Stages of DNA Profiling
Stage 3:• 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 porous gel.
Stages of DNA ProfilingDNA is negatively charged so it is attractedto the positive end ofthe gel.The shorter DNAfragments move fasterthan the longerfragments. DNA is separated onbasis of size.
Stages of DNA ProfilingStage 4:The gel is stained with
ethidium bromide which combines with the DNA fragments to produce a fluorescent image.
Stage 5:The stained gel is exposed
to UV light, photographed and the distribution of fragments is analysed.
In this example, a family consists of a mom and dad, two daughters and two sons. The parents have one daughter and one son together, one daughter is from the mother’s previous marriage, and one son is adopted, sharing no genetic material with either parent. After amplifying the VNTR DNA from each member of the family, it is cut with a restriction enzyme and run on an agarose gel. Here are the results:
Uses of DNA ProfilingDNA profiling is used to
solve crimes, test paternity, identification (immigration, unknown bacteria, virus)
In crime applications, the chances of two people having exactly the same DNA profile is 30,000 million to 1 (except for identical twins).
Who should the police arrest, suspect #1 or #2?
Caution: D
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