Mutations and variation

Gene expression

  • when a gene is ‚switched on or expressed, it is transcribed into an mRNA stand which is then translated into a protein

  • Proteins such as enzymes can control chemical reactions and therefore determine how an organism grows, develops, and functions

  • Only some genes will be expressed at once - this is key to controlling development and cell differentiation

Types of gene mutation

  • a change in the sequence of the DNA can be caused by a change in one or more nucleotides (or base pairs) within a gene

    • Substitution

    • Deletion

    • Insertion

  • If only one nucleotide is affected

    • Point mutation

Effects of gene mutations

  • no effect

    • The protein produced after mutation is still functional

    • Silent/neutral mutations

    • Do not affect phenotype

    • Sometimes called conservative missense mutations

    • Involve incorporation of a similar amino acid

  • Beneficial

    • Rarely the protein synthesised results in new and useful characteristics in the phenotype

      • Immunity to HIV due to a mutation that means a protein in the cell membranes of the person’s cells will not let HIV enter

  • Damaging

    • The phenotype of the organism is affected in a negative way because proteins are no longer synthesised or the proteins synthesised are non functional

    • Interferes with one or more natural processes

    • Nonsense mutation

      • Causes one codon to become a STOP codon so the protein produced is much shorter and thus non functional

    • Non conservative missense mutations

      • Cause the addition of an incorrect amino acid into the primary structure of the protein

      • This amino acid does not have the same properties as the original one so protein has different and non functional structure

Chromosome mutations

  • 4 types

    • Deletion

    • Inversion

    • Duplication

    • Translocation

  • Normally occurs during meiosis

  • gene mutations occur in single genes or sections of DNA whereas chromosome mutations affect a whole chromosome or the number of chromosomes in a cell

  • These can be caused by mutagens and normally occur during meiosis

  • As with single genes mutations, the mutations can be silent but often lead to developmental difficulties

A) UGC

B) TGCTAC

3) the mutation leading to the change in base sequence would change the order of bases causing a disruption in the gene development. This could then mean that when the tertiary structure of the toxin is formed the mutation has caused such a change that the toxin is now incorrectly formed and can no longer function