What are multiple alleles?

Multiple alleles refer to the situation where there are more than two different versions of a gene within a population. This concept expands the traditional understanding of alleles, which are typically thought of in pairs. For example, while a typical gene might have two alleles (one inherited from each parent), the presence of multiple alleles allows for more genetic variation and complexity.

A classic illustration of multiple alleles is seen in the ABO blood group system in humans, where there are three alleles: A, B, and O. These different alleles lead to various blood group phenotypes, showcasing how multiple alleles can enhance genetic diversity and influence traits in an individual. By having multiple alleles for a single gene, organisms can exhibit a range of characteristics, which can be beneficial for adaptation and evolution.

In contrast, the other choices describe concepts that do not accurately define multiple alleles. Two alleles for a gene refers simply to the standard diploid state of genes, alleles located on different chromosomes relates to gene linkage and inheritance patterns, and alleles being always dominant does not capture the variability and complexity of dominance relationships present within a population. Thus, the understanding of multiple alleles profoundly contributes to the study of genetics and heredity.