B3

• Meiosis


  Produces 4 genetically different haploid cells
• Haploid cell


  Has 23 chromosomes
• DNA


  A polymer made up of two strands coiled to form a double helix
• Strands of DNA


  Made from a series of complementary base pairs
• Strands of DNA


  Held together by weak hydrogen bonds
• Cytosine (C)


  Complementary base pair is Guanine (G)
• (G)

  Complementary base pair is C
• Adenine (A)


  Complementary base pair is Thymine (T)
• Thymine (T)


  Complementary base pair is Adenine (A)
• Genome


  All the genetic material of an organism
• Gene


  A section of a DNA molecule that codes for a specific protein
• Protease


  • Breaks down proteins in the nuclear membrane and destroys enzymes that may break down the DNA
• Crushing fruit


  • Breaks down cell walls
• Detergent


  • Breaks down cell membrane
• Salt


  • Clumps the DNA together
• Extracting DNA from fruit

  Crush and add washing up liquid and salt and water, add protease, heat and filter, pour ice cold ethanol into the filtrate
• Ice cold ethanol


  • Precipitates the DNA (DNA is insoluble in ethanol)
• Filtration


  • Removes insoluble material
• Allele


  A version of a gene
• Types of allele


  Dominant and recessive
• Homozygous


  There are two copies of the same allele
• Heterozygous


  There is one dominant and one recessive allele
• Phenotype


  The physical characteristics of an individual
• Gamete


  A sex cell that has a haploid nucleus
• Zygote


  A fertilised egg cell
• Types of variation that influence phenotype

  • Genetic variation
  • Environmental variation
• Benefits of discovering the sequence of bases for all plants and animals

  • Identify useful genes, track evolution, understand diseases, discover new medicines, identify sequences that allow organisms to cope with environmental change
• How the Human Genome Project has contributed to advances in medicine

  • Genes on human chromosome identified, faulty genes can be identified, people can be tested for a genetic disorder, development of gene therapy, personalised medication/counselling can be given
• Causes of genetic variation

  Mutation and sexual reproduction
• Causes of environmental variation

  An organism's environment
• Most genetic mutations do not affect the phenotype