Pedigree Analysis

• Pedigree


  A graphical representation of familial relationships used to investigate the inheritance of genetic traits

  
• The study of human pedigrees faced historical challenges due to variables such as small family sizes and long lifespans, often favoring research on organisms with simpler genetics

  
• Despite these limitations, traditional pedigree analysis has been instrumental in understanding the inheritance patterns of numerous human traits and remains a valuable tool in contemporary genetic studies

  
• Symbols used in pedigree charts

  • Circles represent females, squares represent males
  • Straight horizontal line joins the symbols for the mother and father
  • Vertical line connects with the horizontal line to represent the family line
  • Order of birth is represented by left to right arrangement of symbols
  • Roman numerals represent the generations, Arabic numbers represent the sequence of persons in the same generation

  
• Proband or propositus (proposita, if female)


  The person seeking advice and therefore of interest in the analysis, indicated with an arrow
• Shaded circles or squares


  Indicate that the individuals represented exhibit the trait being studied
• Steps in analyzing a pedigree (Anderson & Gametzky, 1997)

  1. Establish if possible whether the trait is common or rare in the general population

  2. Establish whether the trait is dominant or recessive

  3. Examine whether both males and females are affected

  4. Examine whether fathers pass the traits to sons

  5. Examine whether fathers always pass the allele to daughters

  6. Establish whether any matings are consanguineous (occurring between relatives)