HL 1 Biology

4.4b DNA Profiling

<<The Polymerase Chain Reaction>>

  • PCR (polymerase chain reaction): technique that can be used to “amplify” small quantities of DNA
  • e.g. amplifying fossil DNA with PCR
  • The cycle:
    • 1st stage: denaturing the DNA sample using heat  (separating 2 strands)
    • 2nd: annealing with a primer selected to match a particular target within DNA  (done at cooler temp.)
    • final: extension of primer using DNA polymerase from bacterium adapted to life at high temp. (e.g. Thermophilus aquaticas)
    • process takes place in thermal cycler which can change between the 3 different temperatures per stage
  • PCR primers only bind if theres a complementary sequence to which it can bind
  • no DNA present doesn’t effect PCR

<<Gel Electrophoresis and DNA Profiling>>

  • Gel electrophoresis: includes the separation of charged molecules in an electric field

    • Procedure:
      • samples placed in wells cast in a gel
      • gel immersed in conducting fluid and electric field is applied
      • sample will move in various distances through gel (according to charge and size)
      • gel resists movement of sample; so small molecules can move further than larger ones
    • The # of repeats can be different on paternal and maternal chromosomes;
    • these variations exist in genome and can be used to define “genetic fingerprint” or DNA profile since unlikely for everyone to have same # of repeats in each position in genome
  • DNA profiling: 
    • sample of DNA obtained
    • repetitive sections of DNA are copied using polymerase chain reaction with suitable primers
    • DNA split into fragments using restriction enzymes
    • fragments separated using gel electrophoresis
    • the pattern of bands produced is analyzed

<<Analysis of DNA Profiles>>

  • DNA profiles often used in forensic investigations and disputes over paternity
  • To investigate if suspect committed crime = if DNA sample left at crime scene matches suspect’s, strong evidence he committed the crime
  • To investigate if man is child’s father = need DNA profiles of mother, father and child


PCR and Neanderthals (p.168)

1) 7  differences  

2) As humans and Neanderthals are both classified in the genus Homo, from the data, we can see that the humans and Neanderthals are not the same species. This can be observed as the minimum difference in the human-Neaderthal is greater than the maximum difference in the human-human. But the data does also suggest that the Neanderthals are more related to humans than chimpanzees since there are less differences in the bases of humans- Neanderthals.

3) A limitation to drawing a conclusion from the human-Neanderthal comparison is that there is not enough evidence because of the limited sample of the Neanderthals’s fossil bones.


One thought on “4.4b DNA Profiling

  1. IB 1-7

    Grade 7 A consistent and thorough understanding of the required knowledge and skills, and the ability to apply them almost faultlessly in a wide variety of situations.

    Data-based questions: PCR and Neanderthals page 168

    1. 7

    • data suggests Neanderthals more closely related to humans
    • because of the fewer differences in bases between humans and Neanderthals
    • Minimum difference in human-Neanderthal exceeds maximum human-human difference
    • therefore humans and Neanderthals not the same species

    3. Based on the bones of single Neanderthal/limited support

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