Richard Axel (1946 - present) was awarded half the 2004 Nobel Prize in Physiology or Medicine for his discovery of odorant receptors and research on the organization of the olfactory system. Together with fellow Nobel Laureate Linda B. Buck, Axel cloned olfactory receptors and showed that they belong to a family of proteins called G protein-coupled receptors. By analyzing rat DNA, they estimated that approximately one thousand different genes code for olfactory receptors in the mammalian genome. Axel and Buck have shown that each olfactory receptor neuron only expresses one kind of olfactory receptor protein and that the input from all neurons expressing the same receptor is collected by a single dedicated glomerulus of the olfactory bulb. In addition, Axel and colleagues discovered a process called cotransformation, which allows foreign DNA to be inserted into a host cell to produce proteins.