biology genetics triple paper 1

• genome=

  all the genetic material/DNA of an organism
• DNA structure

  • double helix
  • sugar phosphate backbone
  • pairs of complementary bases
  • bases joined by hydrogen bonds
• protein synthesis

  1. transcription
  2. RNA polymerase binds to DNA near start of gene
  3. RNA polymerase reads bases to make complementary strand of mRNA
  4. translation
  5. mRNA leaves nucleus and binds to ribosome
  6. ribosome reads strand 3 nucleotides (codons) at a time
  7. tRNA, which has complementary anti-codons, delivers appropriate amino acids
  8. amino acids join to create the polypeptide
• meiosis

  produce 4 genetically different haploid daughter cells
• in humans meiosis happens in the reproductive organs
• genotype


  genetic constitution of an organism
• co dominance

  both alleles are expressed in the phenotype
• phenotype


  observable and measurable characteristics of an organism
• asexual reproduction

  doesn't require fertilisation and produces offspring genetically idnetical to the parent
• sexual reproduction

  involves fusion of male and female gametes, increases genetic variation
• allele

  version of a gene
• codon


  sequence of 3 bases, code for specific amino acid in the polypeptide chain
• Mendel...

  carried out breeding experiments on pea plants
• dominant alleles are always expressed
• recessive alleles are only expressed if there are no dominant alleles present
• mutation

  change in order of bases that form the gene
• sexual reproduction advantages

  • increases genetic variation
  • allows for evolution
  • some organisms survive selection pressure
• sexual reproduction disadvantages

  • mate needs to be found
  • process takes longer- time for fertilisation/pollination
  • offspring may have features less advantageous than the parents
• asexual reproduction advantages

  • no mate needed
  • organisms with beneficial characteristics of the parent can be produced
  • fast - reproductive cycle
• asexual reproduction disadvantages

  • no variation
  • selection pressure could affect all organisms
• a gene is

  a small section of DNA on a chromosome, that codes for a particular sequence of amino acids