The genome of the choanoflagellate Monosiga brevicollis and the origin of metazoans.
Early in animal evolution, over half a billion years ago, the genes that code for these three proteins in choanoflagellates recombined by exon shuffling to form the gene that codes for Notch (King et al.
Unlike bacteria and archaebacteria, the choanoflagellate cell has a clearly defined nucleus.
One end of the choanoflagellate cell is adorned with a long whip, or flagellum.
Genetic evidence so far, says Nicole King of the University of California, Berkeley supports the idea that choanoflagellates are the single-cell lineage most similar to multicellular animals.
The distinctive collar made scientists think that choanoflagellates were closely related to multicellular organisms.
Choanoflagellates rely on the collars to trap food, which usually snags on the outside.
Over 600 million years ago, the single-celled choanoflagellates (Latin for "bearing a collar and a whiptail") branched off from the same ancestor that gave rise to animals.
Although also single-celled, choanoflagellates have twice as many genes as yeast.
For example, genes encoding proteins that help cells stick together in modern animals may correspond to genes for proteins used by choanoflagellates to attach to the seafloor.
It is clear that the choanoflagellates
- living representative is monosiga - are the best candidate for the nearest relative of animals," research co-author Rob DeSalle told Discovery News.
It used algorithms to take stock of the presence or absence of specific genes across animals and single-celled organisms such as choanoflagellates
, whose ancestors predate animals.