Issue: Hybrid embryos could potentially help treat serious diseases and advance our knowledge of how cells develop. But the law says that such cells should not be allowed to grow beyond a few days old. Currently there are no plans to create human animal hybrids that could be born and live. These embryos would only live in the lab. But any tissue and organs created in this way for implants would carry the mitochondrial DNA of the egg donating animal into a living human.