single-gene non-Mendelian inheritance

Single-gene non-Mendelian inheritance refers to genetic disorders caused by a single gene but do not follow the typical inheritance patterns described by Gregor Mendel. These patterns can include conditions arising from triplet repeat expansions, mutations in mitochondrial DNA, or issues with imprinted genes.12

Imprinted genes are expressed differently depending on whether they are inherited from the mother or father. For example, if a gene is maternally imprinted, it's usually only expressed when inherited from the father. If that paternal copy has a mutation, the child may not have any functional copies of the gene expressed, leading to a disorder like Prader-Willi syndrome.1

Another non-Mendelian phenomenon is codominance, where both alleles for a gene are expressed equally in a heterozygote. This is seen in the human MN blood group system, where individuals with both M and N alleles have both antigens on their red blood cells. Epistatic genes also play a role, where one gene can mask the expression of another, as seen with the gene for albinism, which can prevent the expression of genes responsible for skin color.345