In genetics, which of these is an allele?

An allele is defined as a variant form of a gene that is responsible for determining specific traits in an organism. Genes exist in pairs or sets, and each member of a pair is referred to as an allele. For example, when considering a gene that influences flower color, one allele might code for red flowers while another might code for white flowers. Therefore, option A accurately describes an allele as a form of a gene that can determine traits.

The other choices do not accurately represent what an allele is. A grouping of genes refers more to a collection of genetic material rather than a specific variant of a gene. A physical trait is the observable expression resulting from genes and alleles but does not define the concept of an allele itself. Lastly, while alleles are associated with DNA, not all types of DNA represent alleles; DNA can also refer to sequences that do not code for specific traits or behaviors.