A heterozygous individual who has one allele for a disease but is not affected by it is known as a carrier. Carriers have one copy of the normal allele and one copy of the disease-causing allele for a particular genetic condition. While they do not exhibit symptoms or develop the disease themselves, they can still transmit the disease-causing allele to their offspring.

When a carrier mates with another individual, there is a 50% chance that they will pass on the disease allele to their children. If the other individual is also a carrier for the same disease, there is a 25% risk that their offspring will inherit both copies of the disease allele and develop the condition.

Carrier status is often identified through genetic testing, particularly when there is a known family history of a genetic disorder. Genetic counseling can be beneficial for individuals who are identified as carriers to understand the risks and implications of passing on the disease allele to their descendants.