4.5 Application of reproduction and genetics

• Stem cells


  Undifferentiated cells that can differentiate into different specialised cells
• Tissue engineering


  The cultivation of cells on a framework of synthetic material to form tissue that can be used to repair tissues or organs
• Pluripotent cells


  Adult cells that can differentiate into most types of cells
• Totipotent cells


  Embryonic cells that can differentiate into all types of cells
• Ethical issues with using embryonic stem cells

  • Opinion that it is the destruction of a potential life
  • Possible long term and unforeseen effects such as premature aging
  • It is an expensive and unreliable technology in mammals
• Genomics


  The study of structure, function, evolution and mapping of genomes
• How genomics could personalise healthcare

  • More accurate diagnosis
  • Better predictions of the effect of drugs
  • Improved design of drugs
  • New and improved treatments for disease
• Human genome project


  The original project to sequence the whole human genome, to improve knowledge and understanding of genetic disorders and improve their diagnosis and treatment
• Sanger sequencing


  Sequenced small sections of DNA and took a long time
• 100K Genome project


  A new project to study the genomes of 100,000 people in the UK, using Next Generation Sequencing which is much faster and can sequence a whole genome in a few hours
• Genome projects have sequenced the genomes of chimpanzees and other primates to look at evolutionary relationships and to conserve species
• Anopheles gambiae mosquito


  A vector for the malarial parasite, sequencing its genome is allowing scientists to study the cause of insecticide resistance and develop new chemicals to reduce the population
• Malaria causes a million deaths per year
• Plasmodium sp


  Sequencing the genome of the parasite that causes malaria is allowing scientists to develop more effective drugs to treat the disease
• Advantages of genetic technology

  • The ability to scan a patient's DNA sample for mutated sequences and to compare the sequence of DNA bases in a patient's gene to a normal version of the gene
  • It may be possible to routinely screen for adult onset disorders such as Alzheimer's disease and some cancers
  • The screening of embryos has been performed to detect the presence of disorders such as cystic fibrosis, Huntington's disease and thalassaemia
  • The use of genetic screening and the value of genetic counselling to give potential parents the options

  
• Disadvantages of genetic technology

  • There are ethical issues in terms of ownership of genetic information, potential discrimination, social stigmatisation and misuse of the data
  • Screening of embryos has led to concerns over choosing alleles to ensure specific characteristics i.e. designer babies
• DNA profiling


  A DNA profile can be read as bands of DNA on an agarose gel, it can be used to compare the DNA from one organism to another by comparing sections of DNA called STRs
• PCR (Polymerase Chain Reaction)


  Used to amplify small sections of DNA rapidly
• PCR process


  1. Heat the DNA to 95oC to separate the two strands

  2. Cool to 50-60 oC to allow the primers to bind to the DNA strands (annealing)

  3. Heat to 70oC allows a thermally stable DNA polymerase to add complimentary nucleotides (extension) by forming the phosphodiester bonds in the sugar-phosphate backbone

  4. Cycle is repeated. After 40 cycles over a billion copies of the target sequence can be produced from just one piece of DNA

  
• Gel electrophoresis


  1. DNA samples are loaded into wells at one end of the gel and a voltage is applied across the gel

  2. DNA is attracted to the positive electrode due to its negative charge on the phosphate group

  3. Smaller fragments find it easier to migrate through the pores in the gel and so travel further than large fragments in the same time

  4. Fragment size can be estimated by running a DNA ladder (which contains fragments of known size) alongside
• Genetic engineering


  The transfer of a gene from one organism into the DNA of another, forming a transgenic organism
• Making insulin using genetic engineering

  1. Identify and obtain the gene

  2. Insertion of the gene into a vector producing recombinant DNA

  3. Inserting the vector (plasmid) into a host cell (bacteria) and identifying the recombinant organisms

  
• Reverse transcriptase


  Collects mRNA from a cell actively producing insulin to form the cDNA from the mRNA, avoiding the need to locate the gene and the problem of restriction enzymes cutting the gene into non-functional fragments

  
• Restriction endonuclease


  Used to cut the required gene out of the DNA of a cell producing insulin, but this gene will contain non-coding introns and bacteria do not contain the enzymes to process the pre-DNA

  
• Concerns with genetic engineering

  • Bacteria may pass antibiotic resistant genes onto pathogenic bacteria
  • Using fragments of DNA could transfer or activate oncogenes

  
• Benefits of genetically modified crops

  • Superior keeping qualities
  • Higher yield
  • Reducing pesticide use
• Concerns of genetically modified crops

  • Spreading genetically modified pollen to wild relatives
  • Unknown effects of eating new protein produced by the crop
  • Reductions in biodiversity
• Gene therapy


  Used to treat genetic disorders by inserting functional DNA sequences into cells to counteract the effect of a defective gene

  
• Duchenne muscular dystrophy (DMD)


  Recessive, sex linked disorder where the mutated dystrophin gene does not produce dystrophin, causing muscle wastage
• Treatment for DMD using gene therapy

  1. The drug contains a sequence of bases complementary to the exon with the deletion mutation

  2. The molecular patch allows the mutated exon to be skipped (exon skipping) during translation and a shorter but more functional protein is formed

  
• Germline therapy


  A rare and controversial therapy where genes are replaced in germline cells so that the changes can be inherited
• Somatic cell therapy


  Treatment alleviates symptoms but is not permanent and will not be inherited. As treated cells become worn and replaced, the new cells do not contain the new gene and so treatment needs to be repeated