Non-Mendelian genetics describes any pattern of inheritance that does not follow the basic gene segregation seen in Mendelian genetics. Non-Mendelian laws of inheritance describe traits that are only linked to one gene on chromosomes. Conversely, Mendelian genetics refer to traits in which two parents both contribute an allele.
In Non-Mendelian genetics, traits do not segregate in the offspring of the parental generation. This type of inheritance is unpredictable and is seen in many disease processes. Mendelian genetics states that each parent contributes an allele to a gene. Therefore, its easy to predict the phenotype of the offspring because the offspring must express one of the two alleles available. Non-Mendelian inheritance is less predictable because it does not follow this pattern.