In genetics, 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 themselves are sequences of DNA that code for proteins and determine various traits in an organism. Each gene can have multiple variants, known as alleles, which arise through mutations and can result in different expressions of a trait.

For example, in the case of a gene that determines flower color in a plant, there may be one allele for red petals and another for white petals. These variations can lead to the observable differences in the plants' flower colors.

Understanding the role of alleles is crucial in genetics, as they contribute to genetic diversity and are fundamental to inheritance patterns, including dominant and recessive traits.

The other options do not accurately define an allele, as they refer to different aspects of genetics or biological structures. A genetic mutation describes a change in the DNA sequence, a node on a chromosome refers to structural components associated with chromosomes, and the physical appearance of a trait pertains to phenotypes, instead of the genetic basis behind variations of traits.