Patterns of Inheritance

Many of these disorders can now be detected byprenatal testing.Genetic counseling can use couples’ pedigreechart and genetic history to determine offsprings’risk of genetic disorders.VARIATIONS ON MENDEL'SLAWS• Mendel was lucky! The relationship ofgenotype to phenotype is rarely that simple– Mendel's principles are valid– However, most characteristics are inherited inways that follow more complex patterns– Variations in dominant/recessive relationships– Traits controlled by numerous genes withcomplex interactions• Variations in dominant/recessive relationship– Complete dominance (simple dominance)• Dominant allele has same phenotypic effect whetherpresent in one or two copies– Incomplete dominance• Crossing 2 different phenotypes produces offspring with a3rd phenotype which is intermediate• Heterozygote exhibits characteristics intermediate betweenhomozygous dominant and homozygous recessive• Dominant allele does not mask recessive– Co-Dominance• Crossing 2 different phenotypes produces a 3rd phenotypein which both traits appear together• Both alleles are fully expressed12