Researchers engineered a mouse with two additional limbs instead of genitals. But why? Moisés Mallo, a development biologist at the Gulbenkian Science Institute in Oerias, Portugal, and his ...

The mouse had a raised, ulcerated mass on the flank of its right hind limb that measured 2.0 cm × 2.5 cm (Fig. 1). The lesion was first observed 15 d previously and had grown rapidly ...

In one instance, after inactivating the gene and then letting the mouse progress through its development ... of certain protostructures that become limbs or genitalia, and they did so by changing ...