What is an allele?

An allele is defined as an alternative form of a gene that can exist at a specific locus on a chromosome. Genes, which are segments of DNA, can come in different versions that may lead to variations in traits or characteristics among individuals. For example, a gene that determines flower color in a plant might have several alleles, resulting in different flower colors. Each allele may encode for different traits, such as purple or white flowers, reflecting variation within the same gene.

In contrast, while the other options mention important genetic concepts, they do not accurately describe what an allele is. A structure made of DNA that contains genes refers to the structure of chromosomes rather than the alleles themselves. A change in the DNA sequence relates more to mutations or variants but does not capture the idea of alleles as forms of a specific gene. Lastly, a method of genetic modification discusses techniques that alter genetic material but does not denote what an allele is. Thus, the chosen answer effectively captures the essence of alleles as variations of genes responsible for different traits.