Inheritance

• genome

  entire DNA of an organism
• gene

  section of DNA that codes for a specific protein
• chromosome

  long strand of DNA found in the nucleus
• structure of DNA

  double helix made of 2 strands linked by complementary bases

  Adenine (A) with Thymine (T)

  Cytosine (C) with Guanine (G)
• structure of RNA

  single stranded

  uses Uracil (U) instead of Thymine
• codon

  3 bases which code for an amino acid
• 2 steps of protein synthesis

  transcription

  translation
• transcription

  DNA helix unzips and exposes bases

  mRNA matches with complementary code

  moves out of nucleus through pores into the cytoplasm
• translation

  ribosome binds to mRNA

  reads 3 bases at a time (codon)

  corresponding anticodon selected on tRNA

  corresponding amino acid made at amino acid binding site

  amino acids form peptide bonds

  process continues until stop codon reached

  protein folds into 3D shape

  ribosome and mRNA can be used again
• allele

  different versions of a gene
• dominant

  only needs one copy of allele to be expressed
• recessive

  needs 2 copies of allele to be expressed
• homozygous

  2 alleles are the same
• heterozygous

  2 alleles are different
• codominance

  2 dominant alleles expressed

  neither is dominant over the other
• polygenic

  characteristics controlled by many genes
• gametes

  reproductive sex cells

  haploid cells (23 chromosomes)

  egg and sperm
• mitosis

  parent cell duplicates all 46 chromosomes

  chromosomes line up in the middle of the cell

  fibres pull chromosomes apart to either side of the cell

  produces 2 genetically identical daughter diploid cells (with 46 chromosomes)
• when is mitosis used

  asexual reproduction

  growth and development

  replacing damaged cells

  cloning
• meiosis

  parent cell duplicates 46 chromosomes

  line up in the middle of the cell

  chromosomes can go to either side and alleles can swap about homologous chromosomes (fertilisation is random)

  cell splits (2 x 46)

  cell splits again (4 x 23)

  produces 4 genetically different daughter haploid cells with 23 chromosomes
• variation

  differences between individuals of the same species
• what causes variation

  random fertilisation / genes

  environmental factors

  combination of both
• mutation

  rare random change in the DNA which ca be inherited

  this can change the sequence of bases in a gene and therefore this codes for different amino acids and therefore changes the protein
• why do most mutations have no real effect

  change in sequence of bases may code for the same amino acid

  occurs in a recessive allele

  happens in non coding DNA
• if a mutation happens in a body cell

  the body cell will die and it wont be passed on and inherited
• if a mutation happens in a sex cell

  the mutation can be passed on
• how can mutations be harmful

  can cause cancers to develop
• how can mutations be beneficial

  can give selective advantages
• how can the incidence of mutations be increased

  ionising radiations (gamma rays, X-rays, UV rays)

  chemical mutagens (tobacco)
• theory of evolution

  life began as simple organisms that over time have become more and more complex
• how can we see the evolution of organisms

  looking at fossils and analysing DNA
• speciation

  2 populations of the same species get geographically separated and evolve

  they change so much that they become 2 separate species
• how bacteria has become resistant to antibiotics

  mutation causes the bacteria to become resistant

  they survive whilst others die

  reproduce asexually which results in all offspring inheriting the resistive allele

  reproduce fast and population grows