DNA profiling Flashcards
What does DNA profiling mean?
Producing image of the patterns in DNA of an individual.
What does genome refer to?
All the genetic material an organism contains.
What are introns?
Large non-coding parts of DNA.
Removed from messenger mRNA before translated into polypeptide chain.
What does satellite DNA refer to?
Short sequences of DNA repeated many times within introns.
What are STRs?
Short tandem repeats.
2-4 bases repeated only 5-15 times
Always appear in same position on the chromosomes.
–> Number of each repeat vary between individuals. (different lengths inherited by each parent)
What is the first step to produce a DNA profile?
Extracting DNA
Must be from tissue sample.
Method needed to extract DNA:
Add detergent to disrupt phospholipid bilayer –> releases DNA
Solution heated in water bath to denature enzymes
Cool mixture –> prevents DNA from breaking down
Filter –> removes membrane fragments
Add protease –> hydrolyses histones
Ice cold ethanol –> nucleic acids insoluble –> DNA clumps up = precipitate.
What is the 2nd step of making a DNA profile?
Strands of DNA cut into small fragments: restriction endonucleases
Different restriction enzymes cut DNA at specific nucleotide sequences –> restriction site/recognition site
Cut defined points in intron
What us the 3rd step of making a DNA profile?
Separating DNA fragments.
Electrophoresis (fragments = clear patterns).
Gel immersed in alkali (separates DNA double strands into single strands)
SS DNA fragments –> transferred on membrane via Southern blotting
Define electrophoresis:
Utilises way charged particles move through gel medium under influence of electrical current.
What is ‘Southern Blotting’?
DNA fragments transferred from the gel to nylon membrane.
What is the 4th step of making a DNA profile?
Hybridisation
Radioactive/fluorescent DNA probes added to excess DNA fragments on membrane.
Bind to complementary strands of DNA under particular conditions of pH and temperature (hybridisation)
DNA probes identify STRs.
What are DNA probes?
Short DNA/RNA sequences complementary to known DNA sequence.
What is the 5th step of making a DNA profile?
Radioactive labels = X-ray images
Fluorescent labels = glows under UV light.
What is present in the vial?
DNA fragments
DNA probes
Free nucleotides
taq DNA polymerase
Primers
What is PCR?
Allows DNA to be replicated
Can produce lots of DNA from tiny sample
Describe what occurs between 90-95?
30 secs
Denatures DNA –> breaks H bonds holding DNA strand
2 strands separate
Describe what occurs at 55-60?
Primers anneal to end of DNA strands
So bonds do not reform
Describe what occurs at 72-75?
Optimum temperature for taq DNA polymerase.
Adds bases to primers –> complementary strands of DNA –> identical to OG sequence
What are the uses of DNA profiling
Criminal investigation
Paternity tests
Classifying species
Immigration cases
Identifying high risk individuals to diseases
