Genetic diversity can arise as a result of mutation

• What is a mutation

  An alteration to the DNA base sequence
• Why might a mutation not lead to change in the amino acid sequence

  Genetic code is degenerate so mutation may end up coding for the same amino acid as the original triplet

  Mutation may occur in intron
• What is a substitution mutation

  When a base in the DNA base sequence is replaced by another

  More likely to be a quiet mutation - meaning no change occurs in the amino acid sequence
• Quiet mutation

  No change occurs in the amino acid sequence
• What is a deletion mutation

  When a base in the DNA sequence is lost

  More likely to be harmful - leads to a frame shift

  The entire amino acid sequence will be different
• Mutagenic agent

  Factors that increase the rate of gene mutation
• Examples of mutagenic agents

  X-rays

  UV light

  Gamma rays

  Chemical - tobacco and alcohol
• What is a polyploidy chromosome mutation

  Where an individual has 3 or more sets of chromosomes instead of 2
• Chromosome non-disjunction

  When chromosomes fail to separate correctly in meiosis resulting in gametes with one more/less chromosomes than normal
• What is meiosis

  A form of cell division that produces four genetically different haploid cells known as gametes
• Haploid cells

  Cells with half the number of chromosomes found in the parent cell
• Meiosis vs mitosis - differences

  Meiosis produces four genetically different cells with half the number of chromosomes as the parent cells

  Mitosis produces two genetically identical cells with the same number of chromosomes as the parent cells
• Meiosis 1


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• Meiosis 2


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• Draw diagrams to show cells after each stage of meiosis


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• Give 2 ways meiosis can produce genetic variation

  Crossing over during meiosis 1

  Independent assortment of homologous chromosomes and sister chromatids

  Result in new combinations of alleles
• Independent assortment

  The production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during metaphase I