Meiosis and mitosis

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  Dominant allele
• Lower cases


  Recessive allele
• Inherited Disorders
• Polydactyly


  • Having extra fingers or toes
  • Caused by a dominant allele
• Cystic fibrosis


  • A disorder of cell membrane
  • Caused by a recessive allele
• How to check for disorders


  • Family trees
  • Screening of embryo
  • Gene therapy
• Meiosis


  1. Cells with chromosomes split and move to opposite poles

  2. Cells divide to form 4 gametes

  3. Each gamete has a single set of chromosomes

  4. Gametes are genetically different
• Meiosis


  • 4 daughter cells
  • Copies of the genetic material are made
  • The cell divides twice
  • All gametes are genetically different
• Mitosis


  1. Chromosomes replicate

  2. Chromosomes line up in the centre of cell

  3. Spindle fibres pull copies to opposite ends of cell

  4. Nuclear membrane dissolves

  5. 2 daughter cells are genetically identical
• Each gene codes for particular sequence of amino acids to make a Specific protein
• DNA


  A polymer made up of small molecules called monomers and is a double helix
• Mitotic spindle fibers are composed of microtubules.