Pedigree Analysis: Six Modes of Inheritance

The inheritance of many monogenic (single-gene) traits can be determined
    by the analysis of family trees (pedigrees)
        Pedigrees show relationships among individuals
        Ex.: Queen Victoria's pedigree shows genetics of Haemophilia A

Six basic Modes of Inheritance
      Distinguish autosomal vs sex-linked conditions
           sex (X) - linked conditions affect predominantly males
           autosomal conditions affect male and females equally

    1. Autosomal recessive
           ex.: Oculocutaneous Albinism (OMIM203100)
                     Batten Disease (OMIM204200): high frequency in Newfoundland
                     PTC tasting (OMIM1720) (Homework)

             Clues: Condition is typically rare (allele frequency is low)
                         Allele is usually present in heterzygous genotypes
                         Condition often occurs in matings of related individuals ("inbreeding")
                         Conditions often "skips generations"

    2. Autosomal dominant
              ex.: Achondroplasia (OMIM100800)
                      Huntington Disease (OMIM143100)
                     Arrthymogenic Right Ventricular Dysplasia, Type 5 (ARVD5) (OMIM 604400)
                            "Newfoundland's sudden-death riddle resolved" (Globe& Mail 29 Feb 2008)
                     Hereditary nonpolyposis colorectal cancer
                      ACHOO syndrome (OMIM100820 ) - photic sneezing
                      Fatal Familial Insomnia (OMIM600072) - a prion disease

              Clues: Allele is usually present in heterozygous genotype
                          Condition appears in every generation

    3. X-linked recessive
              ex.: Haemophilia A (OMIM 306700)
                      Testicular Feminization Syndrome (OMIM300068)
                      Red-Green Colour Deficiency (OMIM306800)

              Clues: Condition occurs predominantly in males
                          Affected males do not have affected offspring
              Criss-Cross inheritance: affected males & females alternate among generations

    4. X-linked dominant
              ex.: Hypophosphatemia (OMIM 307800) (XLH)
 
               Clues: Affected males always pass the condition to daughters
                           Affected females are usually heterozygous

    5. Y-linked