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