mutations

• Mutations are changes to the base sequence in the DNA. Mutations can be caused by addition, deletion and substitution of bases.
• Mutations

  • Mutations are changes to the DNA sequence.
  • Mutations are almost always harmful because they interrupt the normal functioning of a protein.
  • E.g. Cystic fibrosis is a genetic disorder caused by a mutation in the gene for a transmembrane protein.
• Addition mutations

  • Addition mutations are where one or more bases are added to the DNA sequence.
  • E.g. ATCGTT → ATCCGTT
  • In this example, a C is added in the middle of the DNA sequence.
• Deletion mutations

  • Deletion mutations are where one or more bases are removed from the DNA sequence.
  • E.g. ATCGTT → ATCTT
  • In this example, the G is deleted from the middle of the DNA sequence.
• Substitution mutations

  • Substitution mutations are where one or more bases are changed in the DNA sequence.
  • E.g. ATCGTT → ACCGTT
  • In this example, the first T is substituted for a C.
• Mutations

  • Type of mutation
  • Addition
  • One or more bases are added to the DNA sequence
  • ATTCG → ATTACG
  • Deletion
  • One or more bases are removed from the DNA sequence
  • ATTCG → ATCG
  • Substitution
  • One or more bases are substituted in the DNA sequence
  • ATTCG → ATTAG
• causes of mutations:

  Mutagenic agents

  • Mutagenic agents can also increase the rate at which mutations occur.
  • Mutagenic agents include:
  • Chemicals (e.g. bromine and benzene).
  • Exposure to ionising radiation and ultraviolet radiation.
• causes of mutations:

  DNA replication

  • When DNA is replicated, the bases in the DNA sequence are read and copied.
  • There can be errors in the replication process. These errors cause mutations.
  • Mutations caused in DNA replication are spontaneous.
• causes of mutations:

  Chromosome mutations

  • Chromosome mutations can also arise spontaneously during meiosis.
  • Chromosome mutations can affect the number of chromosomes in a developing zygote. This is called aneuploidy.
  • Meiosis is the production of haploid gametes. During meiosis, pairs of chromosomes are separated.
  • Non-disjunction is when chromosome pairs do not separate properly.
• which three processes lead to variation among offspring that have the same 2 parents?

  fertilisation, crossing over and random chromosome assortment.
• body cells are called somatic cells and have double the number of chromosomes found in reproductive cells.
• spores are haploid cells formed only during asexual reproduction and so are not formed by meosis.