From studying the smallest known bacterium, Mycoplasma genitalium, scientists have been able to determine that the essence of life may be coded in as little as 300 genes. Scientists disrupted genes one by one to test if the bacterium still lived. Of the 480 genes in M. Genitalium, roughly 300 were essential to the organism's life functions. The number is inexact because life is "context sensitive." Some genes are switched on in specific circumstances to deal with life-threatening problems such as inadequate nutrients in its environment. Read more at the BBC Online's site: Is Life Just Genes? and Scientists call for life creation debate.