Have you heard of an animal known as a geep? This animal did not occur naturally, and the correct name for it is a goat-sheep chimera. This is an animal that is part goat and part sheep, but not a hybrid. Literally different parts of the animal are goat, and other parts are sheep. It is as if a person spliced the animals together, which is what did occur, through the work of scientists, at the embryonic level.
Natural occurring chimerism is typically occurs when embryos fuse, resulting in one being with different DNA. In order for this to be true the embryos would have to be dizygotic, or non-identical, thus having different DNA.
In nature chimerism can be difficult to detect. Even in humans it can go unnoticed for a lifetime unless there is some reason to conduct DNA testing on different parts of a person's body.
Brindle is an extremely rare color in horses and is believed to be the result of natural occurring chimerism. Other examples might be when an animal has two different colored eyes, patchy colored skin/fur, or is a hermaphrodite, although there are also other reasons why these features may occur.
In sex linked genes where the feature shows up on the opposite gender chimerism can be suspected. In cats this is sometimes the case where a male cat is calico or tortoiseshell, both of which are colors that are genetically sex linked to females.
Marmosets, small new world monkeys, are noted in the animal kingdom as frequently being chimeras, formed by the fusion of two fraternal twins.
One species of anglerfish, known as the sea devil, uses a bizarre method to become its own chimera. An adult male must look for a female fish of the same species. He then bites into her and digests the tissue around the bite, and eventually their circulatory systems merge. The much smaller male's body eventually deteriorates and he grows large testicles, able to fertilize the female at any time.
In April of 2011 scientists released information on a study that showed that chimerism may occur naturally in species that live in a colony, such as corals, anemones, and sponges. They observed, in fact, that chimerism might not be so rare in these organisms, but offered that it simply may be hard to detect such a growth pattern.
In plants chimerism most commonly occurs as the result of human interference, particularly when grafting, but can also present on its own. Chimera plants can be observed to have different colored leaves, flowers, fruits, or other parts. It can be difficult, without testing, to determine if this is a result of a mutation or chimerism.
On the whole chimerism is one of nature's many puzzles, many chimera will live, and die, being undetected for their unique combination of two beings living as one.