What are alleles?

Alleles are different forms of a gene that can exist at a specific locus on a chromosome. Each allele can vary in the nucleotide sequence, leading to different traits or characteristics being expressed in an organism. For example, in the case of flower color in pea plants, one allele might code for purple flowers while another codes for white flowers. Since alleles can produce variations in traits, they play a crucial role in inheritance and the diversity seen within a population.

Identical copies of a gene would refer to alleles that are the same, which does not capture the essence of what alleles are — they must be different forms. Structures that inhibit gene expression are more closely related to regulatory elements such as repressors or silencing RNA, rather than alleles themselves. Lastly, segments of DNA that code for proteins refer to genes in general, whereas alleles specifically denote the variations of those genes.