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Flashcards in DNA technology 2 Deck (18)
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Why is PCR used in genetic fingerprinting

  • Only small amounts of DNA extracted
  • PCR increases the amount
  • So enough DNA is available for comparisons


Describe genetic fingerprinting

  1. DNA extracted from sample
  2. DNA cut into fragments  by RE
  3. DNA fragments separated using electrophoresis
  4. This is according to length/mass
  5. description e.g put mixture in wells on gel and apply electric current
  6. immerse gel in alkaline solution so the 2 strands separate
  7. Cover with nylon to absorb DNA
  8. Radioactive probe is added
  9. Autoradiography is used to identify probes


Why is measuring the no of base pairs a suitable way to measure DNA length

  • DNA made up of base pairs (2 polypeptides)
  • Each base pair is the same length as they occupy the same distance along backbone


Differences between PCR and DNA replication

  1. PCR uses heat to separate strands wheras DNA rep uses DNA helicase
  2. PCR replicates DNA pieces as DNA is cut whereas DNA rep replicates the whole thing


What is a probe and how is it used?

  • Short, single strand of DNA;
  • Has base sequence that is complementary to part of target gene;
  • Will H-bond to strand
  • Fluorescent labelling present
  • So can tell if someone has a specific gene as the probe will bind to it


Ways in which the information obtained from gene probes is helpful to a doctor who is counselling someone with a family history of cancer.

  • Identify carriers of cancer gene
  • Identify which cancer gene present;
  • Identify most effective treatment;


Assuming the base sequence of a specific gene is known. how could we detect a mutation of this gene in a sample of cells 

  • extract DNA;
  • remove specific section using restriction endonuclease 
  • Use sanger sequencing
  • compare with normal sequence for gene;


Suggest how the information acquired through research on biological markers could be used to reduce deaths from cancer.

  • can spot individual at high risk so allows earlier detection of tumours;
  • earlier surgery or drug treatment which increases chances of survival


Explain why the core sequences will vary between individuals

  • RE cuts at specific base sequences
  • RE isolates the introns 
  • Sequence of repeated bases will differ
  • Number of repetition determines DNA fragment length


How can adding DNA fragments size be used to show incomplete digestion by restriction enzymes

  • Large pieces of DNA present;
  • Fragments add up to more than total length of original DNA / plasmid plus inserted DNA;
  • Because this would add undigested to total (original) length;


Methods to find the base sequence of a gene

  • Restriction mapping
  • Then Sanger sequencing


Why should we use the same RE

1. Cut DNA at same base sequence (recognition sequence)

2. So  get fragments with required gene 


When trying to locate which chromosome has a specific gene, why use probes on cells undergoing mitosis 

  • 1. Cells in mitosis so chromosomes visible;
  • 2. So can see which chromosome DNA probe attached to;


Benefits of using a marker e.g glow over genes that confer antibiotic resistance

  • Antibiotic resistance not transferred; 
  • Easier/quicker to identify  modified bacteria


What is a marker gene

  • Gene coding for easily identifiable product
  • Allows scientists to see if (X)  contain transferred gene


Dangers of using antibiotic resistance genes as marker genes

  • Antibiotic resistance gene may be transferred to harmful bacterium;
  • May then be resistant to antibiotic so antibiotic will can no longer be used;


Why does RE X only cuts at these points: A,B,C 

  • Only place where specific base sequence found;
  • Complementary to active site;


Why does a DNA probe with fluorescence only detect allele X

  • Base sequence of probe complementary to DNA of allele X
  • Probe binds by forming hydrogen bonds;
  • So only fluoresces when attached to specific DNA