Autotrophs versus
Heterotrophs
In the haploid bread-mold Neurospora,
wild-type autotrophs are able to
grow
either on complete medium containing a variety of amino acids,
or minimal medium containing only basic CHNOPS salts (carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur).
After
exposure to X-rays, a series of mutant heterotrophs
are obtained that are able to grow only on complete medium:
something
has affected their ability to synthesize amino acids. "Growth"
and
"No Growth" on minimal medium are alternative phenotypes.