What defines an allele?

An allele is defined as an alternative version of a gene. Genes are segments of DNA that code for specific traits, and each gene can have different variations or alleles. For example, a gene that determines flower color in a plant may have a blue allele and a white allele. These alleles can lead to variations in the trait expressed, depending upon the genetic makeup of the individual organism.

The other choices do not accurately describe what an allele is. A complete set of genetic material refers to the genome, which encompasses all the genes and non-coding sequences in an organism. Observable traits of an organism are referred to as phenotypes, which can be influenced by multiple alleles and environmental factors. The organization of genetic material in cells pertains more to chromosomes and cellular structures rather than to the specific variations of genes, which is the primary characteristic of alleles. Thus, the definition of an allele as an alternative version of a gene is fundamental in genetics, ensuring clarity in discussing genetic variation and inheritance.