Cystic Fibrosis

• What inherited disorder is described in the video?

  Cystic fibrosis
• What should you be able to do by the end of the video?

  Describe cystic fibrosis, complete Punnett square diagrams, and express outcomes as percentages or ratios
• What are different versions of genes called?

  Alleles
• What is the difference between dominant and recessive alleles?

  A dominant allele is expressed in the phenotype with one copy, while a recessive allele requires two copies to be expressed
• What is the symbol for the dominant allele for normal cell membrane function?

  Capital C
• What is the symbol for the recessive allele for defective cell membranes?

  Lowercase c
• How many copies of the defective allele must a person inherit to have cystic fibrosis?

  Two copies
• 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 heterozygous and a carrier of the cystic fibrosis allele?

  One copy of the cystic fibrosis allele and one copy of the normal allele
• What is the genotype of a woman who is homozygous for the normal allele?

  Two copies of the normal allele
• How do you construct a Punnett square for cystic fibrosis?

  1. Write down the genotypes of the gametes.
  2. Combine the male and female gametes during fertilization.
  3. Determine the genotypes of the offspring.
• What percentage of the offspring will be carriers if one parent is heterozygous and the other is homozygous for the normal allele?

  50%
• What is the genotype of the offspring that are carriers of cystic fibrosis?

  Capital C lowercase c
• What is the genotype of the offspring that are not affected and not carriers?

  Capital C capital C
• What is the ratio of carriers to non-carriers in the offspring from the cross of a heterozygous and a homozygous normal parent?

  1. 1
• What is the probability that all offspring could be carriers or all could be unaffected?

  These are just probabilities
• What are the expected outcomes when two carriers of the cystic fibrosis allele have children?

  • 25% homozygous normal (not affected)
  • 50% heterozygous carriers
  • 25% homozygous for the defective allele (have cystic fibrosis)
• What is the ratio of offspring from two carriers of cystic fibrosis?

  1 out of 4 not affected, 2 out of 4 carriers, 1 out of 4 with cystic fibrosis
• What will the next video cover after cystic fibrosis?

  Inherited disorder polyductility
• Where can you find plenty of questions on genetic crosses?

  In the vision workbook