What are alleles?

Alleles are defined as different forms of the same gene. Genes are segments of DNA that code for specific traits, and alleles represent the variations of those traits. For example, a single gene might determine flower color in plants, where one allele may code for red flowers and another allele may code for white flowers. The existence of different alleles allows for genetic diversity within a population, which is fundamental to the process of evolution and natural selection.

While other choices may present related genetic concepts, they do not accurately define alleles. For instance, different genes located on the same chromosome pertain to the organization of genetic material rather than variations of a single trait. Identical copies of a gene refer to homozygosity for that gene, and the physical representation of genes generally refers to phenotypes, which describe the observable characteristics that result from the expression of alleles in conjunction with environmental factors. Hence, the correct option emphasizes the variation within a single gene, which is key to understanding how traits are inherited and expressed.