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 does it mean if a person has one copy of the faulty allele?

  They are a carrier
• How is polydactyly caused?

  By a dominant allele
• How many copies of the faulty allele must a person inherit to develop polydactyly?

  Only one copy from one parent
• Why do both individuals with polydactyly show the characteristic?

  Because the polydactyly allele is dominant
• What does a family tree show?

  Only phenotypes, not genotypes
• What is the genotype of person 2 who has cystic fibrosis?

  Lowercase e lowercase e
• What evidence supports that cystic fibrosis is caused by a recessive allele?

  Person 11 has cystic fibrosis, but parents do not
• What would happen if cystic fibrosis was a dominant trait?

  At least one parent would have cystic fibrosis
• What is the chance that persons 7 and 8 would have another child with cystic fibrosis?

  25% or one in four
• What is the genotype of person 3 who has polydactyly?

  Capital P lowercase P
• Why can't person 3 inherit the polydactyly allele from person 1?

  Person 1 does not have polydactyly
• What is the probability that persons 6 and 7 will have a child with polydactyly?

  50% or one in two
• What does the Punnett square show for polydactyly inheritance?

  The probability of offspring having polydactyly
• What are the key differences between cystic fibrosis and polydactyly inheritance?

  • Cystic fibrosis: recessive allele
  • Polydactyly: dominant allele
  • Cystic fibrosis requires two copies to express
  • Polydactyly requires only one copy to express
• How do you determine the genotype of individuals in a family tree?

  1. Analyze phenotypes shown in the tree
  2. Use knowledge of dominant and recessive traits
  3. Apply Punnett squares for probability calculations