US researchers say they have created the world's first genetically modified monkeys by fusing cells from up to six different embryos, in what could be a big advance for medical research.
Until now, rodents have been the primary creatures used to make chimeras, a lab animal produced by combining two or more fertilised eggs or early embryos together.
Scientists have long been able to create "knock-out" mice with certain genes deleted in order to study a host of ailments and remedies, including obesity, heart disease, anxiety, diabetes and Parkinson's disease.
