Why it matters

Many discussions of genetic variation concern which alleles are present and how often they occur. The meaning of an allele depends on its location and the evidence being considered; variation by itself does not establish disease or harm.

A practical example

Suppose a marker can contain either A or G. A record reporting A/G describes the two alleles detected at that position in a typical diploid sample.

An important distinction

An allele is not necessarily an entire gene. It can describe a sequence difference at a much smaller scale. A claim about one allele also should not be stretched into a claim about someone's overall health or identity.

Sources and further reading

The example above is hypothetical. Related cases provide context; they do not imply that every case involved this mechanism.