Cystic Fibrosis

• What inherited disorder is discussed in this video?

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

  Describe cystic fibrosis and complete Punnett squares
• 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 not a carrier of cystic fibrosis?

  Homozygous for the normal allele
• 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 in the offspring from the previous cross?

  1:1
• What does the 50% probability of offspring being carriers indicate?

  It is an average, not a guarantee
• What happens when two carriers of the cystic fibrosis allele have children?

  25% will have cystic fibrosis
• What is the expected ratio of offspring from two carriers of cystic fibrosis?

  1:2:1 for genotypes
• What are the expected genotypes and phenotypes of offspring from two carriers of cystic fibrosis?

  • 25% homozygous normal (not affected)
  • 50% heterozygous carriers
  • 25% homozygous defective (have cystic fibrosis)
• What should you remember about the probabilities of genetic crosses?

  They are averages, not certainties
• What will be covered in the next video?

  • Inherited disorder polyductyly
  • Questions on genetic crosses