Cystic Fibrosis

• What should you be able to complete to show crosses involving cystic fibrosis?

  Punnett square diagrams
• How should you be able to express the outcome of crosses involving cystic fibrosis?

  As a percentage and ratio
• What are different versions of genes called?

  Alleles
• What are the two types of alleles?

  Dominant or recessive
• When will a dominant allele be expressed in the phenotype?

  Even if there's only one copy present
• When is a recessive allele expressed?

  If two copies are present
• What is cystic fibrosis?

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

  By a single gene
• How many alleles does the gene for cystic fibrosis have?

  Two
• What is the normal cell membrane allele in cystic fibrosis?

  Dominant
• What symbol represents the allele for normal cell membrane function?

  Capital C
• What is the defective cell membranes allele in cystic fibrosis?

  Recessive
• What symbol represents the allele for defective cell membranes?

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

  Two
• Where must a person inherit the defective allele to have cystic fibrosis?

  From both of their parents
• What happens if a person has one defective allele and one normal allele?

  They do not have cystic fibrosis
• What is a person with one defective allele and one normal allele called?

  A carrier
• What is the genotype of a man who has one copy of the cystic fibrosis allele and one copy of the normal allele?

  Heterozygous
• If a man is heterozygous for cystic fibrosis, what is he?

  A carrier
• What is the genotype of a woman who is homozygous for the normal allele?

  She does not have cystic fibrosis
• What must you write down first when constructing a Punnett square?

  The genotypes of the gametes
• Why are chromosomes single in gametes?

  Because of meiosis
• In a cross between a carrier male and a homozygous normal female, what percentage of the offspring will have the genotype capital C lowercase c?

  50%
• In a cross between a carrier male and a homozygous normal female, what percentage of the offspring will have the genotype capital C capital C?

  50%
• In a cross between a carrier male and a homozygous normal female, what is the ratio between carriers and not affected?

  One to one
• Are numbers from the punnett squares probabilities or certainties?

  Probabilities
• What percentage of offspring will be affected if both parents are heterozygous?

  25%
• What percentage of offspring are carriers if both parents are heterozygous?

  50%
• In terms of ratios, what is the ratio of not affected, carriers, and those with cystic fibrosis when both parents are carriers?

  One to two to one
• What inherited disorder will be covered in the next video?

  Polydactyly