mitochondrial dna: DNA necessary for mitochondrial replication. It is inherited only through the maternal line.

merozoite: A stage in the life cycle of some parasites that enables the organism to disperse and infect additional cells within the host.

parasite: An organism that lives on or in another organism (or host). A parasite does not help the host; in fact, it typically harms the host.

parasitology: A branch of biology dealing with parasites.

pathology: A branch of medical science involving the cause, the process, the anatomic effects, and the consequence of disease.

recombinant dna: A composite molecule of DNA that has been formed in the laboratory with DNA from separate sources.

recombinant dna technology: The applied science of separating, producing, and recombining segments of DNA or genes.

ribosomal proteins: The proteins that form a ribosome. The DNA that codes for these proteins is species specific and is used to identify the species of tissue (e.g., to determine if blood is human blood or blood of a particular species of animal).

ribosome: A cellular entity responsible for manufacturing all cellular protein.

transgenic: An organism whose genome contains one or more genes from another species (e.g., pigs containing human genes to facilitate human reception of pig heart valves).

vaccine: A substance given to an individual to produce resistance to disease or infection.

xenograft: An organ or tissue taken from one species and transplanted into another species. Generally, a xenograft refers to an animal organ or tissue dial is transplanted into a human (e.g., a pig heart valve).