Cystic Fibrosis

• Cystic fibrosis


  An inherited disorder of cell membranes
• Cystic fibrosis


  • Controlled by a single gene
  • Has two alleles
• Normal cell membrane function allele

  Dominant, symbol capital C
• Defective cell membrane allele

  Recessive, symbol lowercase c
• To have cystic fibrosis, a person must inherit two copies of the defective allele
• Person with one defective allele and one normal allele

  Carrier of the cystic fibrosis allele
• Punnett square for a carrier parent and a non-carrier parent

  1. Write down gamete genotypes

  2. Combine gametes to get offspring genotypes

  3. Calculate percentages of offspring genotypes
• Possible outcomes: 50% carriers, 50% not affected
• Punnett square for two carrier parents

  1. Write down gamete genotypes

  2. Combine gametes to get offspring genotypes

  3. Calculate percentages of offspring genotypes
• Possible outcomes: 25% not affected, 50% carriers, 25% with cystic fibrosis</b>
• Probabilities are averages, actual outcomes may vary