family trees

• Family tree


  Also called a family pedigree
• Cystic fibrosis


  A recessive inherited disorder
• Recessive allele


  Represented by lowercase f
• Dominant allele


  Represented by capital F
• Homozygous recessive genotype


  Two lowercase f alleles
• Homozygous dominant genotype


  Two capital F alleles
• Heterozygous genotype


  One capital F allele and one lowercase f allele
• Carrier


  Has one cystic fibrosis allele and can pass it on to children
• Family pedigree symbols


  • Circles represent females
  • Squares represent males
  • Unshaded shapes = no condition
  • Shaded shapes = have condition
  • Half-shaded shapes = carrier
• Determining genotype from family pedigree

  1. Homozygous recessive = disease

  2. Heterozygous = carrier

  3. Homozygous dominant = unaffected
• Generations in family pedigree

  • Top row = parents
  • Second row = children
  • Bottom row = grandchildren
• Horizontal lines between individuals


  Indicates they are a couple
• Individuals connected by horizontal lines are unrelated but partners of members of the main family
• Calculating probability of baby having cystic fibrosis

  1. Look at genotypes of parents

  2. Draw Punnett square

  3. 1 in 4 chance of baby having disease