Answer:
The presence of a nucleus
Explanation:
Living organisms have been classified into a large group called DOMAIN. The basis of this classification is the possession or not of a membrane-bound housing that encloses the organism's genetic material. This housing is called NUCLEUS. Based on this, organisms were either classified as EUKARYOTES or PROKARYOTES.
Eukaryotic organisms, in addition to the possession of other membrane-bound cellular organnelles, possess a membrane bound nucleus that surrounds their genetic material. Prokaryotic organisms do not have these membrane-bound nucleus, instead their genetic material is found naked in a region of their cytoplasm called NUCLEOID.
