A sheep–goat chimera (sometimes called a geep in popular media) is a chimera produced by combining the embryos of a goat and a sheep; the resulting animal has cells of both sheep and goat origin. A sheep-goat chimera should not be confused with a sheep-goat hybrid, which can result when a goat mates with a sheep.
The first sheep-goat chimeras were created by researchers at the Institute of Animal Physiology in Cambridge, England by combining sheep embryos with goat embryos. They reported their results in 1984. The successful chimeras were a mosaic of goat and sheep tissue. The parts that grew from the sheep embryo were woolly. Those that grew from the goat embryo were hairy.
In a chimera, each set of cells (germ line) keeps its own species' identity instead of being intermediate in type between the parental species. Because the chimera contains cells from two different genetic individuals, and each of these arose by normal mating, it has four parents. In contrast, a hybrid has only two parents.
A sheep-goat chimera may be fertile, but it passes on either sheep or goat genes, depending on whether its reproductive organs were formed from the goat embryo or from the sheep embryo (i.e., whichever germ-line formed the ovaries or testes).
The term shoat is sometimes used for sheep-goat hybrids and chimeras, but that term more conventionally means a young piglet.
The most popular way of identifying a geep is to simply look at the animal's tail. A geep's tail extends horizontally from the base of the spine combining the characteristics of a sheep's and goat's tail.