Pedigree Analysis: Six Modes of Inheritance

The inheritance patterns 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 genetic inheritance of Hemophilia A

Six basic Modes of Inheritance
    Dominant vs Recessive transmission     
    autosomal vs sex-linked traits
           X - linked traits affect predominantly males
           Y - linked traits affect only males
           autosomal traits affect males & females equally

    mtDNA - linked affect both, passed only through females   


Consult Online Mendelian Inheritance in Man (OMIM) for examples of 'genetic' traits
                N.B.: Many classical human genetic conditions are not determined by a single gene locus:
                       e.g., eye
colour

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

             Clues: trait is
usually rare (allele frequency is low)
                         Allele is usually present in heterozygous genotypes
                         trait often occurs in matings of related individuals
                                consanguineous marriage - at least one ancestor in common, versus
                               
"inbreeding" - consanguineous marriages occur more frequently than expected
 
                         trait often "skips generations"
              Ascertainment Bias in use of pedigree data

    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 (HNPCC)
                      ACHOO syndrome (OMIM100820 ) - photic sneezing
                      Fatal Familial Insomnia (OMIM600072) - a prion disease
                     
              Clues: Allele is usually present in heterozygous genotype
                          trait must appear in every generation

                
Marker-assisted genetic diagnosis (IG1 15.22)

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

 
              Clues: trait occurs predominantly in males
                          Affected males usually do not have affected offspring
                         "Criss-Cross inheritance": affected males & females alternate between generations

               X-linked Co-Dominant: the genetics of tortoiseshell & calico cats

 
  4. X-linked dominant
              ex.:
Hypophosphatemia (OMIM 307800)
 

               Clues: Affected males always pass the trait to daughters
                           Affected females are usually heterozygous

    5. Y-linked
             ex.: Zinc-Finger Protein, Y-linked (ZFY) (OMIM490000)
                    Sex-determining Region Y (SRY) (OMIM480000)
                    Hairy Ears (OMIM425500) not Y-linked: a sex-limited trait

                   Clues: trait occurs in all male descendants, and only males
                               Phenotypes are typical of males

     6. mtDNA-linked
             ex. Matrilineal descendants of Queen Victoria           
                   Leber Hereditary Optic Neuropathy (OMIM535000)
             mitochondrial DNA
(mtDNA) a cytoplasmic (non-nuclear) genome

                   Clues: occurs in all descendants of any female
                              Affected males do not transmit trait
                              Typically associated with muscular & neurological conditions                             
             Wide use in genealogy: the "Daughters of Eve" in Newfoundland



Homework: In the following pedigrees, which modes of inheritance can be ruled out?
                         Which individual(s) allow you to do so?
                      Which are possible? Which is most likely? Explain.
                         Write out the genotypes of each of the individuals.

Pedigree 01

Pedigree 02
Pedigree 03
Pedigree 04
Pedigree 05
Pedigree 06
Pedigree 07
Pedigree 08
Pedigree 09
Pedigree 10
Pedigree 11
Pedigree 12


All text material ©2019 by Steven M. Carr