Having parts of different origins. In medicine, refers to a person, organ, or tissue that contains cells with different genes than the rest of the person, organ, or tissue. This may happen because of a mutation (genetic change) that occurs during development, or as a result of a transplant of cells, organs, or tissues from another person or from a different species. In the laboratory, a chimeric protein can be made by combining two different genes. For example, a chimeric antibody is made by joining antibody genes from two different species, such as human and mouse.