Family trees

• What is cystic fibrosis caused by?

  A recessive allele
• What must a person inherit to have cystic fibrosis?

  The faulty allele from both parents
• What genotype does a carrier of cystic fibrosis have?

  One copy of the faulty allele
• How does a person with cystic fibrosis inherit alleles?

  They inherit the faulty allele from both parents
• What is the cause of polydactyly?

  A dominant allele
• How many copies of the polydactyly allele are needed to show the characteristic?

  One copy of a dominant allele
• What does a family tree show?

  Phenotypes, not genotypes
• Why is cystic fibrosis considered a recessive disorder?

  Both parents must be carriers for it to appear
• What are the key characteristics of cystic fibrosis and polydactyly inheritance?

  Cystic Fibrosis:

  • Caused by a recessive allele
  • Requires two copies of the faulty allele

  
  

  Polydactyly:

  • Caused by a dominant allele
  • Requires only one copy of the allele to express the trait
• What is the significance of family trees in genetics?

  • Show phenotypes of individuals
  • Help determine inheritance patterns
  • Indicate carriers of recessive alleles
• How do you use a Punnett square for cystic fibrosis and polydactyly?

  Cystic Fibrosis:

  • Both parents are carriers (e.g., eE x eE)
  • Probability of offspring with cystic fibrosis is 25%

  
  

  Polydactyly:

  • One parent affected (e.g., Pp x pp)
  • Probability of offspring with polydactyly is 50%