Nontraditional Inheritance

The “rules” of segregation of alleles originally defined by Gregor Mendel explained much of the phenomena associated with inheritance and have been dogmatically applied in the field of genetics. However, there are situations in which the rules of Mendelian inheritance cannot explain observed phenomena. A variety of molecular mechanisms have been identified that explain certain phenomena that are not easily explained by traditional Mendelian patterns of inheritance. These non-Mendelian mechanisms differ on a molecular basis, but can be described as a group by the term “nontraditional mechanisms of inheritance” or “nontraditional inheritance.” Stated simply, nontraditional inheritance refers to the pattern of inheritance of a trait or phenotype that occurs predictably, recurrently, and in some cases familially, but does not follow the rules of typical Mendelian autosomal or sex chromosome inheritance. Examples discussed in this chapter are the triplet repeat expansion mutations, and genomic disorders including genetic imprinting, mitochondrial inheritance, and multi-allelic inheritance.