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 are the two types of alleles mentioned?

  Dominant and recessive
• How is a dominant allele expressed in the phenotype?

  It is expressed with one copy present
• When is a recessive allele expressed?

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

  Cell membranes
• How many alleles control cystic fibrosis?

  One 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
• What do half of the male gametes carry in this scenario?

  The cystic fibrosis allele
• What is the outcome for 50% of the offspring in this cross?

  They are carriers of the defective allele
• What is the first step in constructing a Punnett square?

  Write down the genotypes of the gametes
• What is the ratio of carriers to non-carriers in this cross?

  1 to 1
• What do the numbers in the Punnett square represent?

  Probabilities of offspring genotypes
• What is the expected percentage of offspring that are carriers when two carriers cross?

  50% of the offspring
• What percentage of offspring are homozygous for the normal allele in this cross?

  25% of the offspring
• What percentage of offspring have cystic fibrosis when two carriers cross?

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

  • 25% homozygous normal (not affected)
  • 50% heterozygous carriers
  • 25% homozygous defective (have cystic fibrosis)
• What is the next topic to be covered in the following video?

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

  In the vision workbook
• What is the significance of probabilities in genetic crosses?

  They indicate potential outcomes, not certainties