In the case of most symbiotic relationships found in nature, one partner is fully dependent on the other. These are referred to as 'obligate' relationships. An interesting example of this is lichen. Lichen is the result of a successful symbiotic partnership between algae and fungi. There is an obvious evolutionary advantage to partnerships; lichen is capable of surviving in environments where either the algae or the fungi would be unable to live independently. Scientists want to know if either partner-species sacrifices anything to be part of the relationship. For example, in a newly married couple's home, duplicate kitchen appliances would be naturally discarded. So is there a genetic analogy to this housekeeping arrangement? Colorado University recently answered this question for us. Research revealed that, in the case of lichen. the fungus cannot survive without the algae. When the partnership is made, the fungus loses the energy-creating gene from its mitochondria. It requires the algae to supply this missing gene. The sacrifice, however. comes with added evolutionary advantages.