This packaging of the four meiotic products makes genetic analysis particularly simple. The ease with which baker's yeast can be maintained as either haploid cells or diploid cells is another characteristic that makes them attractive to geneticists. People have used yeast, undoubtedly one of the earliest domesticated organisms, for controlled fermentation of food and drink and for leavening in baking throughout recorded history. Today, they are also used in a variety of commercial fermentation and biomass conversion processes. Ethanol is a valuable alternative to petroleum as a fuel and as a raw material for the manufacturing of many important commercial chemicals.
Yeast is also good food.
It is rich in protein and is an uncommonly good source of the B vitamins. It provides a valuable source of nutrients that are important in low-meat or vegetarian diets. But while few emanations from the kitchen are quite as tantalizing as the yeasty aroma of baking bread, most people agree that pure yeast tastes pretty bad. Other genera of yeast also have practical uses. Some can use hydrocarbons, such as petroleum, as a carbon source.