Cystic Fibrosis

• What inherited disorder is discussed in this video?

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

  Describe cystic fibrosis and complete Punnett squares
• What are alleles?

  Different versions of a gene
• What is the difference between dominant and recessive alleles?

  Dominant alleles are expressed with one copy
• What is the symbol for the dominant allele for normal cell 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 have 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 heterozygous for cystic fibrosis?

  One copy of each allele (C and c)
• What is the genotype of a woman who is homozygous for the normal allele?

  Two copies of the normal allele (CC)
• What is the first step in constructing a Punnett square?

  Write down the genotypes of the gametes
• What percentage of offspring will be carriers when a heterozygous man and a homozygous normal woman have children?

  50% will be carriers
• What is the genotype of the offspring that are carriers?

  Capital C lowercase c
• What is the ratio of carriers to non-carriers from the cross of a heterozygous man and a homozygous normal woman?

  1:1 ratio of carriers to non-carriers
• What happens when two carriers of the cystic fibrosis allele have children?

  They can have offspring with cystic fibrosis
• What are the expected genotypes of offspring from two carriers of cystic fibrosis?

  25% CC, 50% Cc, 25% cc
• What is the probability of offspring being homozygous for the defective allele?

  25% probability
• What are the outcomes of a cross between two carriers of cystic fibrosis?

  • 25% homozygous normal (CC)
  • 50% heterozygous carriers (Cc)
  • 25% homozygous defective (cc)
• What are the key points about probabilities in genetic crosses?

  • Probabilities indicate expected outcomes
  • Actual results may vary
  • All offspring could be carriers or unaffected
• What will be covered in the next video?

  Inherited disorder polyductyly
• Where can students find questions on genetic crosses?

  In the vision workbook linked above