Mutations HT: Inheritance, variation and evolution: Biology: GCSE (9:1)

• Gene


  A small section of DNA that controls a specific characteristic by coding for a specific protein

  
• Bases


  A specific organic section of a nucleotide that contains nitrogen, there are four different types of bases in a DNA polymer

  
• C, G, A and T


  The letters that represent the four different types of bases found on a strand of DNA

  
• Nucleotide


  A small structural unit of DNA, composed of a common sugar and phosphate group with one of four different bases attached to the sugar

  
• Repeating nucleotides

  The DNA polymer is made up of repeating nucleotide units with different arrangements of the bases C, G, A and T

  
• Sequence of three bases

  The genetic code for an amino acid also called a codon or triplet, this arrangement of three bases leads to the formation of one specific amino acid

  
• Amino acids

  The building blocks of proteins, the sequence of amino acids determines the shape and function of the overall protein

  
• Proteins

  Building blocks of cells and tissues, made up by a specific order of amino acids which in turn is coded for by a specific sequence of DNA

  
• A change in the specific sequence of DNA


  Can affect the sequence of amino acids produced, which can subsequently affect the overall shape and function of a protein

  
• Protein chain


  When a chain of amino acids is completed it folds up to form a specific shape, enabling proteins to do their jobs as enzymes, hormones or structural collagen

  
• Mutation


  A change in the sequence of DNA that can result from copying errors during cell division or exposure to ionising radiation, chemicals or viruses

  
• Types of mutation

  Base substitution, insertion, deletion or inversion

  
• Base insertion or deletion


  Where a single base is added or removed in a DNA sequence, which could lead to the translation of a different amino acid

  
• Base substitution or inversion


  Where a single base is swapped or where the order of several bases change, which could lead to the translation of a different amino acid

  
• Insignificant effect of mutations

  Most mutations have no effect on the shape of the protein and even if the shape changes slightly it may not affect the protein's function

  
• Significant effects of mutations

  Mutations can have a significant effect in rare cases, an altered enzyme may not fit a binding substrate or an altered structural protein may lose its strength

  
• Genetic variants

  Changes in DNA as a result of mutation which can alter the sequence of base triplets and therefore alter the sequence of amino acids in coding DNA

  
• Phenotype


  The observable properties or characteristics of an organism

  
• Non-coding DNA


  Regions of DNA that do not code for proteins, but are responsible for gene expression and can switch genes on and off
• Effect of genetic variants on non-coding DNA

  Altering the sequence of non-coding DNA could result in genes that are typically off being switched on or vice versa