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 membranes allele

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

  Carrier of the cystic fibrosis allele
• Punnett square for parents who are carriers

  1. Write down genotypes of gametes

  2. Combine gametes during fertilization
• Offspring genotypes from carrier parents

  • 25% homozygous normal (CC)
  • 50% heterozygous carriers (Cc)
  • 25% homozygous defective (cc)
• Offspring phenotypes from carrier parents

  • 25% not affected
  • 50% carriers
  • 25% have cystic fibrosis
• Probabilities of offspring genotypes/phenotypes are averages, actual outcomes can vary