Biomedical Engineering Reference
In-Depth Information
descendants of a bikont might evolve to lose one flagellum, or unikonts might
evolve to grow a second flagellum. If this were to happen, the phylogenetic
distinction between unikonts and bikonts would be lost.
As it turns out, the early division of eukaryotes into unikonts and
bikonts is one of the most brilliant achievements in modern taxonomy.
Whether a modern class eukaryotes has gained or lost a flagellum makes
little difference. In fact, Class Fungi, a subclass of Class Unikonta, has
evolved to lose its flagellum. No matter; the ancestry of Class Fungi can
be traced to Class Unikonta. Three fused genes (carbamoyl phosphate
synthase, dihydroorotase, aspartate carbamoyltransferase) are uniquely
characteristic of Class Unikonta. Two fused genes (thymidylate synthase
and dihydrofolate reductase) uniquely characterize Class Bikonta.
The morphologic property dividing Class Eukaryota into unikonts and
bikonts is shadowed by a genetic property that draws the equivalent
taxonomic division.
The value of the eukaryotic flagellum (undulipodium) as a taxonomic
divider is witnessed again in Class Opisthokonta. Class Opisthokonta is a
subclass of Class Unikonta that contains Class Choanozoa, Class Animalia
and Class Fungi. The opisthokonts all descend from an organism with its
undulipodium extending from the rear (from the Greek “opisthios,” meaning
rear and “kontos” meaning pole). The rear-ended flagellum distinguishes the
members of Class Opisthokonta from classes that have a flagellum extending
from anterior or lateral sides.
Chapters 16 through 37 will demonstrate that the human eukaryotic
pathogens can be classified in terms of their inherited class properties.
