allotype

An allotype is a variant of a protein or other molecule that is encoded by a different allele at a single genetic locus. Allotypes are typically found in polymorphic systems, where multiple alleles exist at a given locus. These variants can differ in their amino acid sequence, resulting in different protein structures and functions. Allotypes are often used in serological typing and genetic studies to identify and classify individuals based on their genetic makeup.

The term "allotype" was introduced by the British geneticist J.B.S. Haldane in 1935. It is distinct from an allele, which is any variant form of a gene at a specific locus, and an isotype, which refers to different forms of the same protein produced by different genes. Allotypes are particularly important in the study of blood groups and other immune system-related proteins, where they can influence antigenicity and reactivity.

In human genetics, examples of allotypes include the different variants of the ABO blood group system, where the A and B antigens are allotypes of the same gene locus. These allotypes can lead to different blood types, such as A, B, AB, or O, which are determined by the presence or absence of specific sugars attached to the core protein structure.

Allotypes play a crucial role in understanding genetic diversity, disease susceptibility, and immune responses. They are also used in forensic science and paternity testing to identify individuals based on their unique genetic profiles. The study of allotypes continues to be an active area of research in genetics and immunology.