Patterns of inheritance are usually more complicated than what is predicted by Mendelian genetics. Explain four possible exceptions to Mendelian genetics involving the inheritance patterns of a single gene and provide an example of each.

Please find the explanation of the four possible exceptions to Mendelian genetics below.

Explanation:

Genetics, generally, has to do with how genes are inherited or transferred from parents to offsprings. Gregor Mendel, however, explained this concept in his principles of inheritance called Mendelian genetics. There are, however, exceptions to this mendelian principle called Non-mendelian pattern of inheritance i.e patterns of inheritance that do not follow Mendel's principles. Four of them are explained below:

- Incomplete dominance- This non-mendelian inheritance pattern occurs when one allele of a gene does not completely mask its allelic pair, but instead forms an intermediate phenotype. This is in contrast with Mendelian genetics that proposes complete dominance. For example, a red and white flower produce a pink flower (intermediate).

- Codominance- This is another non-mendelian inheritance where two alleles of a gene are simultaneously expressed. For example, roan cattles is a combination of both red and white hairs.

- Multiple alleles: Some traits in a population are controlled by more than two alleles, as explained in mendelian inheritance. Examples of trait controlled by multiple alleles is height in humans.

- Sex-linked inheritance: Some traits are controlled by genes on sex chromosomes i.e. X and Y chromosomes. This genes exhibit inheritance pattern that are different from Mendel's. Example is haemophilia disease controlled by an affected gene on the X-chromosome.