mutations and gene editing

• Mutation


  Any change to the DNA or RNA base sequence of a cell or virus
• Types of gene mutations


  • Substitution mutations
  • Insertion mutations
  • Deletion mutations
• Point mutation


  Changes one base in a DNA sequence
• Substitution mutation


  One or more nucleotides in a DNA sequence is replaced by another nucleotide
• Insertion mutation


  One or more nucleotides is added to a DNA sequence
• Deletion mutation


  One or more nucleotides are removed from a DNA sequence
• Single-nucleotide polymorphism (SNP)


  A single nucleotide in a gene is changed, resulting in a different amino acid in a protein
• Polymorphism


  The occurrence of two different phenotypes within a population
• Degeneracy


  One amino acid can be coded by more than one codon
• A base substitution mutation does not affect the protein if the mutated codon codes for the same amino acid
• If a base substitution mutation mutates a codon to code for a different amino acid or a stop codon, then a different protein sequence is produced
• Sickle cell anaemia is an example of a single-nucleotide polymorphism caused by a single base substitution in a gene required for making haemoglobin
• Frameshift mutation


  Insertions or deletions of nucleotides (which are not in multiples of three), changing all of the codons after the mutation
• Polypeptides produced by frameshift mutations are unlikely to function, as many codon changes produce a different sequence of amino acids
• Mutagen


  An agent that causes permanent, heritable changes to the DNA of cells
• Examples of mutagens


  • High energy radiation (UV, X-rays, gamma-rays, alpha-particles, beta-particles)
  • Chemicals (polycyclic aromatic hydrocarbons, alkylating agents)
• Mutations occur randomly in any location within a genome, though mutations vary according to nucleotide
• There is no natural mechanism for making a deliberate mutation to create a new allele for a gene, and change a trait
• Consequences of mutations


  • Neutral
  • Beneficial
  • Harmful
• Germ cells


  Cells that develop into gametes such as sperm or eggs
• Somatic cells


  All cells which are not reproductive cells
• Mutations in somatic cells are not passed on to offspring, as somatic cells are not involved in sexual reproduction
• Mutations to proto-oncogenes in somatic cells can result in cancer, which is uncontrolled cell division
• Natural selection


  The differential survival due to the inheritance of traits that make an individual more likely to survive and reproduce
• Genetic variation is a requirement for evolution by natural selection
• Most mutations are neutral or are harmful to the individual, though beneficial mutations do occur
• Natural selection will increase the survival and reproduction of individuals with alleles, produced by mutation, which make them better adapted to survive and reproduce
• There are many commercially available genetic tests which provide a range of information on a person's genome, including information on potential health and disease risk
• One possible impact is that, without expert interpretation, this information could be problematic