DNA Profiling Flashcards
How is a DNA profile created? [basic explanation - 4]
- DNA sample obtained
- PCR amplifies specific regions of DNA
- Fluorescent tag added to all DNA fragments so can be viewed under UV light
- Gel electrophorisis seperates DNA fragments according to length
How can a DNA profile be analysed?
- DNA fragments appear as bands under UV light making up a DNA profile
- Two DNA profiles can be compared to see how similar the pattern of bands on the gel is
What do the bands on a DNA profile being in the same position mean?
The two chromosomes have the same number of STRs at a locus
What do the bands on a DNA profile being in different positions?
The two chromosomes have a different number of STRs at a locus
What are the 6 possible uses of DNA profiling?
- Forensics
- Evolutionary relationships between organisms
- To prevent interbreeding in animals and plants
- ID purposes
- Paternity dispute
- Forensics
How can DNA profile be used in forensics? 2
- Compare DNA sample from crime scene to DNA samples from possible suspects
- If samples match links person to crime scene
How can DNA profiling be used in paternity disputes? (3)
- 1/2 of DNA comes from each parent
- STRs are inherited like alleles - offspring receives 1 repeated sequence randomly from each parent
- More bands on 2 DNA profiles matching - the more closely related the 2 people are
Why should interbreeding in plants and animals be prevented? 2
- Decreases gene pool so increased risk of genetic disorders
- Could cause health, productivity and reproductive problems
What is the flaw in DNA profiling?
DNA profile only analyses a few repeated sequences out of genome - less likely to be unique to each person
What is the purpose of PCR? 2
- To amplify DNA for there to be enough to make a DNA profile
- By making millions of copies of specific regions of DNA
What does the PCR reaction mixture contain? 4
- DNA primers
- Free DNA nucleotides
- DNA polymerase
- DNA sample
What are primers?
Short DNA sequences complementary to bases adjacent to STR
Why are primers needed in PCR?
To provide an OH group as the starting point for DNA polymerase to attach bases in creating a new DNA strand
Why are 2 different primers needed in PCR? 2
- Each primer binds to one end of the DNA segment to be amplified
- The sequence at the two ends is different
Explain the steps of PCR - 8
- Reaction mixture is heated to 95c, breaking the hydrogen bonds between the two DNA strands so they separate into 2
- Mixture is cooled to 55c to allow primers to anneal [bind to] to strands at the start of the STR with complementary base pairing
- Heated to 70c – the optimum temperature for DNA polymerase
- DNA polymerase lines up free nucleotides alongside the DNA template strand so new complementary strands are formed
- Two copies of the DNA fragment formed as 1 cycle of PCR is complete
- Cycle starts again as mixture is heated to 95c and so all 4 DNA fragments are used as templates
- Procedure repeated multiple times
- Each PCR doubles amount of DNA
