...to reveal the fundamental processes that make magnetic sensing robust. We will use molecular dynamics and spin dynamics simulations to elucidate the fundamental physical and chemical requirements for cryptochrome-based magnetoreception and to make predictions for critical experimental tests of the hypothesis in migratory animals. Project 1 will study the molecular origins of the interactions of cryptochrome with its key interaction partners. Project 2 will use computer simulations to guide and interpret the results of experimental studies of the magnetic sensitivity of cryptochromes in vivo and ex vivo and to understand more completely the operation of a radical pair magnetoreceptor.