Which statement best describes an allele?

An allele is defined as a version of a gene that occupies a specific position on a chromosome. Genes can exist in multiple forms, and these variants are what we refer to as alleles. For instance, a gene that determines flower color in a plant may have different alleles that produce red or white flowers. Each organism inherits two alleles for each gene, one from each parent, which can be the same (homozygous) or different (heterozygous). This genetic variation is crucial for the diversity of traits in a population and plays a key role in inheritance.

The other options do not accurately capture the definition of an allele. A chromosome refers to a structure within the cell that contains many genes, not specifically an individual variant of a gene. The complete set of genes would refer to the genome, which encompasses all genetic material in an organism. Environmental factors can influence traits, but they are not alleles themselves; alleles specifically pertain to hereditary variations in genes.