What is "homoplasmy"

Homoplasmy \Ho"mo*plas`my\, n. [Homo- + Gr. ? anything formed, fr. ? to form, mold.] (Biol.) Resemblance between different plants or animals, in external shape, in general habit, or in organs, which is not due to descent from a common ancestor, but to similar surrounding circumstances.

n. the presence of the same mutation in all copies of mitochondrial or plastid DNA within a single cell or individual

Homoplasmy is a term used in genetics to describe a eukaryotic cell whose copies of mitochondrial DNA are all identical. When in normal and healthy tissues, all cells are homoplasmic. Homoplasmic mitochondrial DNA copies may be normal or mutated; however, most mutations are heteroplasmic (only occurring in some copies of mitochondrial DNA). It has been discovered, though, that homoplasmic mitochondrial DNA mutations may be found in human tumors.

The term may also refer to uniformity of plant plastid DNA, whether occurring naturally or otherwise.