Pedigree analysis

• Pedigree


  Diagrams used to show how individuals are related to one another (similar to family trees)
• Pedigree analysis


  A way of finding out the type of inheritance of a characteristic by following the inheritance pattern over two or more generations
• Pedigree Symbols


  • Genotype
  • Phenotype
• Genotype


  Colours can also be used to represent genotype of individuals
• Genotype


  • Brown hair (B) is dominant allele and Blond hair is recessive allele
• Phenotype


  Sometimes pedigrees show phenotypes instead of genotypes
• Phenotype


  • Brown hair (B) is dominant allele and Blond hair is recessive allele
  • Brown symbol below represent brown hair and yellow symbols represent blond hair
  • Shading can represent individual who has the trait
• Type of Inheritance


  • Recessive
  • Dominant
  • Sex-linked
  • Autosomal
• Recessive Inheritance


  • A recessive trait will only be expressed if both alleles are recessive (homozygous)
  • One copy must have been passed from each parent
  • If parents do not show the trait but offspring do, then it must be recessive
  • The trait is not expressed in heterozygotes
• Dominant Inheritance


  All affected individuals have at least one affected parent
• Autosomal Inheritance


  • Both males and females can be affected
  • Any individuals can inherit from either father or mother
• 1. Linked Recessive Inheritance


  • Mostly males are affected
  • All sons of an affected female will be affected
  • None of sons of affected male are affected
• Individual's Alleles


  Can use pedigree to determine alleles an individual has passed on to offspring
• Individual's Alleles


  • Brown hair (B) is dominant allele and Blond hair is recessive allele
• Pedigree Analysis - Hemophilia

  1. Is Hemophilia a dominant or recessive gene?

  2. Is it an autosomal or sex-linked disorder?

  3. Who are carriers of the Hemophilia gene?
• From the pedigree chart, Hemophilia is a recessive gene
• From the pedigree chart, Hemophilia is a sex-linked (X-linked) disorder
• From the pedigree chart, the carriers of the Hemophilia gene are Victoria, Alice, Alice's daughters, Beatrice, Beatrice's daughter
• Pedigree Analysis - Cystic Fibrosis

  1. Is Cystic Fibrosis a dominant or recessive gene?

  2. Is it an autosomal or sex-linked disorder?
• From the pedigree chart, Cystic Fibrosis is a recessive gene
• From the pedigree chart, Cystic Fibrosis is an autosomal disorder