In scientific terms, a chimera is essentially a single organism composed of genetically distinct cells, which can result in male and female organs, two different blood types, or subtle variations in form. Animal chimeras are produced by the merger of multiple fertilized eggs. Normally, chimerism is not visible on casual inspection; however, it has been detected in the course of proving parentage. Another way that chimerism can occur in animals is by organ transplantation, giving one individual tissues that developed from two different genomes. For example, a bone marrow transplant can change someone's blood type. Continue reading to see more.