Genetics of Multiple Alleles: Concept and Function

Abstract

Mendelian genetics revealed only two alternative forms of a gene called alleles. The concept has evolved with the identification of more than two alternative forms of a gene, commonly referred to as multiple alleles. There are several traits that are governed by multiple alleles, such as ABO blood group system in humans, coat color in rabbits, and self-incompatibility in crop plants. The test of allelism is a very common practice to establish the relationship between alleles of the same or different genes. The inter-mating among different mutants helps to confirm whether mutations are allelic or non-allelic. The structural allelism determines whether two mutations are present at the same or different site in DNA and functional allelism determines whether two mutations are present in the same gene or in different genes. The concept of multiple alleles should not be confused with pseudoalleles and with pseudogenes. Pseudoalleles are two genetically linked genes with similar effects located close to each other on the chromosome, on the other hand, pseudogenes are nonfunctional copies of the functional genes. To understand the allelic relationships among and between genes is always a subject of interest. Therefore, in this chapter, the concept, function, and importance of multiple alleles are discussed.