Gene Mutation

• What is a gene mutation?


  A change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide.
• What does the DNA base sequence determine?

  The amino acids that make up a protein.
• What does a gene mutation result in?

  A change in the polypeptide that the gene codes for.
• Why do most mutations not alter the polypeptide or only alter it slightly?

  As the genetic code is degenerate and so a single amino acid may be coded for by more than one codon.
• What are the different ways a mutation can occur?

  Deletion of nucleotides, or substitution of nucleotides.
• What is deletion of nucleotides?


  A mutation that occurs when a nucleotide is randomly deleted from the DNA sequence.
• What may a deletion mutation change?


  The amino acid that would have been coded for.
• What is a frameshift mutation?

  A mutation that causes a knock-on effect by changing the groups of three bases further on in the DNA sequence.
• What kind of mutation is a deletion mutation?

  A frameshift mutation.
• What is a substitution mutation?


  A mutation that occurs when a base in the DNA sequence is randomly swapped for a different base.
• How is a substitution mutation different to a deletion mutation?

  A substitution mutation will only change the amino acid for the triplet in which the mutation occurs and won't have a knock-on effect whereas deletion will.
• What three forms can substitution mutations take?

  Silent mutations, missense mutations, and nonsense mutations.
• What is a silent mutation?

  A mutation that does not alter the amino acid sequence of the polypeptide due to it being degenerate.
• What is a missense mutation?

  A mutation that alters a single amino acid in the polypeptide chain.
• What is a nonsense mutation?

  A mutation that creates a premature stop codon and causes the polypeptide chain produces to be incomplete and effect the final protein structure and function.
• What are mutagenic agents?

  Environmental factors that increase the mutation rate of cells.
• What are examples of mutagenic agents?

  High-energy radiation, ionising radiation, and toxic chemicals.
• What is non-disjunction?


  When chromosomes or chromatids spontaneously do not split equally during anaphase resulting in gametes not having the right amount of chromosomes.
• What is polyploidy?


  When organisms (most of the time plants) have three or more sets of chromosomes rather than the usual two.
• What is aneuploidy?


  When the number of individual chromosomes changes resulting in a gamete having one more or fewer chromosomes (downs syndrome).