Pedigree Analysis: Six Modes of Inheritance

The inheritance of many monogenic (single-gene) traits can be determined
    by the analysis of family trees (pedigrees) (IG1 15.22)
        Pedigrees show relationships among individuals
        Ex.: Queen Victoria's pedigree shows genetic inheritance of Hemophilia 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 usually rare (allele frequency is low)
                         Allele is usually present in heterozygous genotypes
                         Condition often occurs in matings of related individuals
                                consanguineous marriage - at least one ancestor in common
                                "inbreeding" - consanguineous marriages occur more frequently than expected
                          Conditions often "skips generations"

    2. Autosomal dominant
              ex.: Achondroplasia (OMIM100800)
                      Huntington Disease (OMIM143100)
                     Arrthymogenic Right Ventricular Dysplasia, Type 5 (ARVD5) (OMIM604400)
                            "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 must appear in every generation

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

              Clues: Condition occurs predominantly in males
                          Affected males usually 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