Cystic Fibrosis

• What are alleles?

  Different versions of a gene
• How are dominant alleles expressed?

  Always expressed in the phenotype
• When is a recessive allele expressed?

  When two copies are present
• What type of disorder is cystic fibrosis?

  A disorder of cell membranes
• How is cystic fibrosis controlled genetically?

  By a single gene with two alleles
• What is the symbol for the normal allele in cystic fibrosis?

  Capital C
• What is the symbol for the defective allele in cystic fibrosis?

  Lowercase c
• What must a person inherit to have cystic fibrosis?

  Two copies of the defective allele
• What do we call a person with one defective allele and one normal allele?

  A carrier of the cystic fibrosis allele
• What is the genotype of a man who is a carrier of cystic fibrosis?

  Heterozygous with one normal and one defective allele
• What is the genotype of a woman who is homozygous for the normal allele?

  Two normal alleles
• How do you determine the offspring's genotypes from a Punnett square?

  By combining the gametes of the parents
• What percentage of offspring will be carriers when a heterozygous man and a homozygous normal woman have children?

  50%
• What is the ratio of carriers to non-carriers from the cross of a heterozygous man and a homozygous normal woman?

  1:1
• What is the probability of offspring being affected by cystic fibrosis from a cross of two carriers?

  25%
• What are the genotypes of the offspring from two carriers of cystic fibrosis?

  25% homozygous normal, 50% carriers, 25% affected
• What does the ratio 1:2:1 represent in the context of cystic fibrosis inheritance?

  Offspring genotypes from two carriers
• What are the key points about cystic fibrosis inheritance?

  • Controlled by a single gene
  • Two alleles: dominant (C) and recessive (c)
  • Affected individuals have two recessive alleles (cc)
  • Carriers have one dominant and one recessive allele (Cc)
  • Punnett squares can predict offspring genotypes
• What are the probabilities of offspring genotypes from two carriers of cystic fibrosis?

  • 25% homozygous normal (CC)
  • 50% carriers (Cc)
  • 25% affected (cc)
• What is the significance of probabilities in genetic crosses?

  • Probabilities indicate potential outcomes
  • Actual results may vary from predictions
  • Useful for understanding inheritance patterns