BIOLOGY TOPIC 6 - INHERITANCE, VARIATION AND EVOLUTION

• mitosis


  formation of 2 genetically identical daughter cells
• meiosis


  formation of 4 genetically nonidentical daughter cells
• sexual reproduction


  cells spilt by meiosis

  male and female gametes fuse (sperm and egg/pollen and ova)

  offspring are nonidentical

  2 parents
• asexual reproduction


  1 parent

  no gamete fusion

  cells divide by mitosis

  offspring are clones
• how does meiosis work?

  chromosomes replicate

  cell splits twice

  4 genetically different gametes (haploid cells)
• DNA


  double helix polymer
• genes


  small sections of DNA

  code for sequence of amino acids that code for specific protein
• chromosomes


  contain many genes

  23 pairs
• what is DNA made of?

  nucleotides

  contain phosphate, sugar and base
• protein synthesis


  template taken from DNA and leaves nucleus

  template used to guide protein synthesis on ribosomes in cytoplasm

  amino acids delivered by carrier molecules to protein chain
• mutation


  permanent change in DNA's nucleotide sequence
• alleles


  different forms of the same gene
• genotype


  combination of alleles an organism has
• phenotype


  physical characteristics
• cystic fibrosis


  recessive disorder of cell membranes
• polydactyly


  dominant disorder resulting in extra fingers or toes
• advantages of embryonic screening

  prevent suffering

  IVF embryos

  financial screening
• disadvantages of embryonic screening

  discrimination

  expensive

  ethics

  'designer babies
• variation


  differences in characteristics of individuals in a population
• speciation


  when phenotypes of two populations change so much they can no longer breed to produce fertile offspring
• natural selection


  genetic variation

  survival of the fittest - those better suited to environment will survive

  breeding - individuals with best survival chances are more likely to breed

  genetics for survival passed onto next generation
• evolution


  gradual change in a species over time
• selective breeding


  when humans choose animals and crops to breed based on genetic characteristics
• selective breeding

  (long answer)

  - choose parents who strongly display desired characteristics

  - breed chosen parents

  - from resultant offspring choose offspring that best display chosen characteristics

  - breed chosen offspring

  - repeat process until all offspring show desired characteristics
• uses of selective breeding

  usefulness

  appearance
• dangers of selective breeding

  reduced variation

  inbreeding
• genetic engineering

  (long answer)

  - enzymes used to 'cut' desired gene out of chromosome

  - same enzyme used to 'cut' a vector, usually bacteria or virus

  - vector used to insert gene into required cells

  - if gene delivered to cells before they differentiate, all cells in developed organism will have gene and show characteristic
• uses of genetic engineering


  transferring genes into animals, bacteria or plants
• advantages of genetic engineering

  improves food production

  prevents inherited disease
• disadvantages of genetic engineering

  ethical issues

  long term impacts on human health

  reduced biodiversity
• cloning plants by tissue culture

  small groups of cells extracted from plant and placed in a growth medium

  division of cells eventually leads to formation of clone of parent plant
• cloning plants by cuttings

  branch is cut from parent plant

  plant hormones used to encourage growth of roots from cutting

  cutting is planted and grows into new plant
• adult cell cloning


  remove nucleus from unfertilised egg cell

  egg cell injected with nucleus of adult body cell belonging to animal to be cloned

  electric shock given to egg to stimulate division

  once embryo has grown it is implanted into surrogate mother

  embryo continues to develop in womb of surrogate
• Darwin's theory of natural selection

  all species have evolved from simple life forms
• reasons for slow acceptance of Darwin's theory

  lack of evidence

  religious beliefs

  genes hadn't been discovered yet
• what did Lamarck discover (he was wrong)?

  Theory of acquired characteristics

  (giraffes)
• speciation long answer


  two populations become geographically isolated

  populations show genetic variation

  different environments mean that natural selection operates differently on populations

  variation continues until populations are unable to breed to produce fertile offspring

  results in 2 different species
• speciation definition


  formation of new species
• 3 ways of forming fossils

  preservation when decay isn't possible

  hardening soft materials

  mineral replacement
• why is the fossil record incomplete?

  many early life forms were soft-bodied, so they didn't leave behind many traces