And because mitochondria descend from a bacterium that , about 2 billion years ago , became symbiotic with the cell from which animals and plants are descended , they have their own , small chromosomes .
Madonna adds that gaga " seems to have had a challenging upbringing , and so I can see where she would also have that kind of connection , a symbiotic relationship with gay men . "
Her examination of a grass species growing in the hot and hostile environment of a geyser field in yellowstone park showed that its heat tolerance was conferred by a virus that lives in a fungus which is , itself , symbiotic with the grass : no virus , no heat tolerance .