Non-Mendelian traits do not follow Mendel's laws for the genetic inheritance of traits, which hold that biological traits are determined by individual genes that follow dominant-recessive inheritance patterns, explains TutorVista.com. Some phenomena that result in non-Mendelian inheritance include polygenetic inheritance, epistasis and gene imprinting, notes Pleasanton Unified School District.
In the case of polygenetic inheritance, multiple genes along chromosomes are involved in the expression of a trait, explains Pleasanton Unified School District. Traits following this inheritance pattern tend to exhibit a large amount of variation among a population. Two examples of traits determined by polygenetic inheritance are human height and human eye color shade, both of which exist in a wide variety of expressions.
Epistatis occurs when one gene's expression masks the expression of another. This is different from the genetic concept of dominance, which involves single genes rather than different genes interfering with one another, notes Pleasanton Unified School District.
Gene imprinting is a phenomenon by which a methyl group is added to a gene copy, rendering it inactive so that the other copy is the one expressed. The gene that gets imprinted depends on which one came from the maternal or paternal parent, explains Pleasanton Unified School District.
Traits following these patterns of inheritance differ from those following Mendelian laws in that dominance determines gene expression in Mendelian traits, notes Pleasanton Unified School District. The dominant version of the trait, or the allele, is the one expressed in an individual possessing either two copies of the dominant allele or one dominant and one recessive copy. The recessive trait is only expressed if the individual has two recessive copies of the gene.