Which best describes a "carrier" in the context of genetics?

The term "carrier" in genetics specifically refers to an individual who possesses one copy of a recessive allele for a trait but does not exhibit the phenotype associated with that trait. This means that while the individual carries the genetic information for the recessive trait—meaning they have the allele—they do not display the associated characteristics due to the presence of a dominant allele masking the recessive effects. Carriers play a vital role in the inheritance of genetic traits, especially when two carriers mate, as they have the potential to pass on the recessive allele to their offspring, leading to offspring that may express the recessive trait if they inherit the recessive allele from both parents.

In contrast, individuals with a visible trait are exhibiting a dominant phenotype and may not carry any recessive alleles. Those with two recessive alleles would express the recessive trait rather than be classified as carriers. Furthermore, individuals who can only pass on dominant traits would typically not have any recessive alleles to contribute, thus not fitting the definition of a carrier.