What is an organism that is heterozygous for a harmful trait?

Answer 1

Assuming the deleterious trait is recessive, the individual would be called a carrier.

Answer 2

An example of an organism that is heterozygous for a harmful trait is a carrier of a genetic disease like sickle cell anemia. In this case, the individual has one copy of the normal allele and one copy of the disease-causing allele, which can lead to the manifestation of the disease in offspring if they inherit two copies of the harmful allele.