1. an individual with a gene for a recessive trait that is unexpressed in that individual but that may be expressed in offspring if the individual reproduces with another carrier of the same gene.

2. an individual who is infected with a pathogen for a disease and is capable of infecting others but does not develop the disease.

3. an individual who has a mutation in a gene that conveys either increased susceptibility to a disease or other condition or the certainty that the condition will develop. A BRCA1 mutation carrier, for example, is a person who carries an altered BRCA1 gene (see BRCA1 and BRCA2). This alteration is responsible for significantly raising the likelihood that the person, if female, will develop breast or ovarian cancer. See also obligate carrier.