Allotype refers to the variation of a protein within a species. Some synonyms for allotype include isoallotype, allozyme, and genetic polymorphism. Isoallotype refers to a particular variation of a protein that arises due to a difference in the amino acid sequence. Similarly, allozymes also refer to alternative forms of enzymes resulting from genetic variation. Genetic polymorphism encompasses all types of genetic variation that exist within a population. It can include variations in nucleotide sequence, structural variation or variations in the number of copies of a gene. Though these terms differ slightly, they are used interchangeably in research and literature to refer to the same concept.