In an attempt to study the spine, scientists in Portugal accidentally created a mouse embryo with an extra pair of hind legs, where its genitals should be — and the strange turn of events could improve our understanding of human embryo development, metastatic cancer, and more.  What’s new? There’s a lot we still don’t understand about what goes on in the womb — how a single cell becomes an entirely new organism. In an attempt to clear up some of this mystery, scientists at the Gulbenkian Science Institute in Portugal decided to study the gene Tgfbr1, which codes for a protein already known to play a role in embryo development.  “[We were] very surprised.” Moisés Mallo For their study, published in Nature Communications, the team inactivated the Tgfbr1 gene in mouse embryos that were halfway through development. They expected that this might have some effect on the rodents’ spines. What they weren’t expecting was for one of their embryos to grow an extra pair of hind limbs where its external genitalia should have been. “[We were] very surprised,” lead researcher Moisés Mallo told Newsweek. But… how? Prior to this, …