Unit 8

• Genetic Drift

  • Random changes in allele frequencies which are not caused by environment.
  • Mating and fertilisation are random events. By pure chance some allele may be passed on whilst others are not.
  • This occurs in small populations and is a mechanism for evolution.
• Inversion - a group of bases becomes separated from the DNA sequence and rejoins, but in reverse order.
• Duplication - one or more bases are repeated. This creates a frameshift downstream
• Translocation of bases - a group of bases becomes separated from the DNA sequence of one chromosome and becomes inserted into the DNA sequence of a different one.
• Protooncogenes stimulate the cell cycle, by producing proteins to increase cell division. A mutated protooncogene is an oncogene and increases the speed of the cell cycle, so it is less regulated and less well 'checked'.
• Tumour suppressor genes, slow the cell cycle in order to regulate it and prevent uncontrolled cell division and hence the formation of abnormal cells. A mutated tumour suppressor gene is particularly disadvantageous, as not only can cell division not be regulated and checked, but abnormal cells cannot be killed - apoptosis.
• Genetic Counselling

  Advising patients about the risks of genetic disorders. I.e. advising about screening (for carriers of mutated alleles). If the results of the screening are positive, then advice on treatment/ prevention can be given.
• Gene Therapy

  • Overriding recessive disorders with dominant alleles.
  • 'Silencing' dominant alleles with single strands of DNA which hybridise with the DNA base sequence causing the problem. In both cases a vector is required: viruses, liposomes