DNA Profiling Flashcards
How do we compare DNA
We compare DNA by comparing STR’S (short tandem repeats), found in introns of DNA. DNA is made of exons (code for proteins) and introns.
What is short tandem repeats
Short tandem repeats are regions of repeated introns that are different for everyone.
Function of introns
Function of introns are regulatory sequences for genes, tell Exons when to get copied and how much to get copied.
Why do we compare DNA fingerprints
We compare DNA fingerprints for:
Crime scene analysis
Paternity testing
Gene mutation testing
How to do DNA profiling
Do DNA profiling by:
Obtaining DNA e.g small sample of crime scene
Obtain DNA fragments using restriction enzymes or PCR
Use gel electrophoresis to analyse DNA Samples
Separate DNA by gel electrophoresis
Compare DNA with blotting and probing
How do we separate STR
We separate STR with restriction nucleases, they cut at specific sequences of DNA and nowhere else. E.g AGA would cut only at AGA but no where else. Then could use another to cut CTG sequences. If there was STR sequence which had AGA just upstream and CTG just downstream, it will extract STR. In general, if restriction sites are either side of STR, it will be cut away from genome.
Where are restriction enzymes/restriction endonucleases extracted from
Restriction enzymes are extracted from bacteria.
What is gel electrophoresis
Gel electrophoresis separates DNA (STR’S)fragments based on their size, like a sieve. Smaller particles fall out quicker
How is gel electrophoresis carried out
Gel electrophoresis is carried out by
Cut DNA with restriction enzymes
Load DNA into agarose gel (extract of seaweed)
Add phosphate buffer (DNA is negatively charged)
Add electric current ( DNA moves towards positive side, anode in gel electrophoresis)
Smallest DNA fragment moves quicker and further because not caught in molecular sieve
Southern blot and add DNA probe
What can you do when STR’S are separated in electrophoresis?
When STR’S are separated, you can compare the banding patterns between individuals, look for similarities between the size, position and total number of bands
How can you make radioactive fragments visible following electrophoresis
You can make radioactive fragments visible following electrophoresis by transferring onto nylon sheet and using X ray
Why can a restriction enzyme only cut at a specific base sequence
Restriction enzyme can only cut DNA at a specific base sequence because only the specific base sequence has substrate which fits into enzymes active site
