Inheritance, variation and evolution

• Mitosis


  Leads to two identical daughter cells
• Meiosis


  Leads to four different daughter cells
• In mitosis, the cells are diploid
• In meiosis, the cells are haploid</b>
• Gametes


  • X in women
  • Sperm in men
• Plant gametes


  • Eggs in stigma
  • Pollen on stamen
• Meiosis


  1. Chromosomes line up

  2. Chromosomes sort down the middle

  3. Crossing over

  4. Divide into two

  5. Divide into two again
• Asexual reproduction


  Genetically identical population
• Advantages of sexual reproduction

  • Genetically diverse population
  • Better protected from diseases
• Disadvantages of asexual reproduction

  • Genetically identical population
  • Whole population susceptible to disease
• Advantages of asexual reproduction

  • Only one parent required
  • Energy conserved
• DNA


  • Made from bases that fit together (A-T, C-G)
  • Has a sugar phosphate backbone
  • Double helix structure
• Gene


  Stretch of DNA
• Genome


  All the genes in a body
• Protein synthesis


  1. DNA sequence codes for amino acid sequence

  2. Amino acid chain folds into protein
• Proteins


  • Responsible for everything in the body
  • Enzyme active sites are very specific
• Mutation


  • Change in the amino acid sequence
  • Can have a big impact on protein function
• Non-coding DNA


  Junk DNA that is not useful
• Gamete


  Sex cell
• Allele

  Different versions of a gene
• Dominant


  Need one gene to express characteristic
• Recessive


  Need two identical recessive genes to express characteristic
• Homozygous

  Genes are the same
• Heterozygous


  Genes are different
• Genotype


  Genes you have
• Phenotype


  Collection of characteristics
• Genetic cross


  Work out chances of disease/phenotype being passed on
• Genetic conditions


  • Polydactyly
  • Cystic fibrosis
• Embryo screening


  • Test embryos before implantation
  • Only implant healthy embryos
  • Can find genetic match for sibling
• Chromosomes


  • 23 pairs (46 total)
  • Determine sex (XX female, XY male)
• Identical twins


  • Have same genotype but different phenotypes
• Genotype


  Genetic information
• Environment


  Influences phenotype
• Mutation


  Mistakes in DNA copying
• Natural selection


  • Gradual change over time
  • Individuals better suited to environment more likely to survive and reproduce
• Life evolved from simple unicellular organisms over 3 billion years
• Evidence for evolution


  • Fossils
  • Rapid changes in bacteria
• Evolutionary tree


  Shows how species are related and when they diverged
• Speciation


  One species splitting into multiple species due to geographical separation
• Speciation example


  • Darwin's finches on Galapagos islands