A2-LEVEL AQA BIOLOGY NOTES 
TOPIC 7: differences in dna between individuals of the same species can be exploited for identification and diagnosis of heritable conditions

< BACK TO TOPIC INDEX

DNA Probes = short, single-stranded pieces of DNA

• DNA fragments are complementary to the piece of DNA that is being investigated
  
• Probe is labelled:
  
  • Using a radioactive marker
    
  • Fluorescent marker that emits a colour on exposure to UV light
    
• Copies of the probe will anneal to any complementary single strand
  
• Probes are useful in locating specific alleles of genes, for example:
  
  • Locate a desired gene for genetic engineering
    
  • Identify the same gene on different genomes
    
  • Identify the presence or absence of an allele - including screening patients for heritable conditions, drug responses or health risks
    

DNA hybridisation = technological process used to measure degree of difference between two strands of DNA

• Useful in phylogeny
  
• One DNA strand is labelled and mixed with another unlabelled strand
  
• In warm temperatures the two strands hybridise into double strand
  
• Similar strands bind more strongly
  
• Therefore more energy required to separate them again
  

Use in medicine

• Genetic profiling is a new technology that is beneficial in medicine
  
• Can identify heritable diseases in patients that are very young and begin treatment before symptoms begin to manifest
  
• Reduces long-term implications of the disease
  
• Treatment is customised to the specific allele that the patient carries
  
  • Therefore more likely to be effective and could have fewer side effects