Ans: When many variations of a gene are present in a population, multiple alleles exist. Though human organisms are diploid, some alleles are present in the human chromosome with more than two variations. Multiple alleles are the result of spontaneous mutation. For example, the human eye colour and blood group system are examples of multiple alleles. More than two variations of human eye colour are caused by the pigmentation of the iris and the frequency of light scattering. Different variants of the human blood group are caused by red blood cell type, plasma and antigens of the red blood cell.