chromosome mutation

• Chromosome mutations


  Changes in the number of chromosomes
• Nondisjunction in meiosis


  1. Chromosomes/chromatids do not separate equally in anaphase

  2. Results in gametes with incorrect chromosome number
• Polyploidy


  Whole additional set(s) of chromosomes
• Aneuploidy


  Change in number of just one chromosome
• Aneuploidy example


  • Down syndrome
• Polyploidy nondisjunction in meiosis 1

  1. Chromosomes fail to separate equally

  2. One cell gets all chromosomes, other cells have no chromosomes

  3. Meiosis 2 proceeds normally, resulting in diploid gametes
• Polyploidy nondisjunction in meiosis 2

  1. Meiosis 1 normal, but chromatids do not separate equally in one cell in meiosis 2

  2. Results in diploid gamete
• Aneuploidy nondisjunction in meiosis 1

  1. One chromosome pair fails to separate equally

  2. Results in gametes missing or having an extra copy of that chromosome
• Aneuploidy nondisjunction in meiosis 2

  1. Meiosis 1 normal, but chromatids of one chromosome do not separate equally in meiosis 2

  2. Results in gametes missing or having an extra copy of that chromosome
• Polyploidy is usually fatal in humans but common in plants
• Down syndrome is caused by an extra copy of chromosome 21