BY5.4 Mutations

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  • a change in the amount, arrnagement or structure of DNA in an organism
  • mutation rates are very smal
  • they can affect a single gene or a whole chromosome
  • most occur in body cells
  • only mutattions that occur in gametic formation are passed on
  • spontaneous random events provide the source of material for natural selection pressures - evolution
  • organisms with a short life cycle have a greater rate of mutations
  • the rate is increased by ionising radiaiton and mutagenic chemicals

Mutagens and Mutation rate:

  • mutations occur naturally
  • the rate increases when exposed to mutagens (e.g. x rays, gamma radiation, UV light, chemicals)
  • mutagens that cause cancer are known as carcinogens
  • mutagens don't cause mutations
  • an increased exposure to mutagens increases the rate of mutations occuring

mutations happen in 2 ways:

  • DNA is not copied properly before cell division
    • gene mutation
  • chromosomes are damaged and break, when they break they would normally repair but they may not repair properly
    • chromosome mutaton

Gene mutations:

  • a change in the structure of a DNA molecule
  • it affects the differnet alleles of a gene
  • a gene can mutate but rates vary from gene to gene
  • changes in the base pairs within the genes take the form of duplication, insertion, deletio, inversion or substitution os bases
  • this results in the formation of a modified polypeptide

How can mutations change in phenotype?

  • genetic code made up of specific sequence of nucleotides on DNA molecules
  • any change to nucleotides or rearrangement produces incorrect sequences of amino acids for the protein to make

Sickle cell anemia:

  • result of substitution in the gene that produces haemoglobin
  • replacement of one base in the DNA molecule…


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