Non-Mendelian inheritance refers to any pattern in which traits do not segregate in accordance with Mendels laws. Mendel's laws describe the inheritance of traits linked to single genes on chromosomes in the nucleus. In Mendelian inheritance, each parent contributes one of two possible alleles for a trait, and if the genotypes of both parents in a genetic cross are known, Mendel's laws can be used to determine the distribution of phenotypes expected for the population of offspring.
However, there are several situations in which the proportions of phenotypes observed in the progeny do not match the predicted values. Non-Mendelian inheritance plays a role in several diseases that affect the processes. Non-Mendelian inheritance involves the inheritance of traits that have a more complex genetic basis than one gene with two alleles and complete dominance. Some examples of non-Mendelian inheritance include:
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Incomplete Dominance: Two alleles may produce an intermediate phenotype when both are present, rather than one fully determining the phenotype.
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Codominance: Both alleles are simultaneously expressed in the heterozygote.
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Multiple Allele Traits: A gene that is controlled by more than two alleles.
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Polygenic Traits: Traits that are controlled by multiple genes.
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Extranuclear Inheritance: A form of non-Mendelian inheritance in which genes are located outside the nucleus, such as in mitochondria or chloroplasts.
Non-Mendelian inheritance is important in human genetics, which is controlled by multiple genes and whose inheritance does not follow the rules of Mendelian genetics.
