Cytologists have long observed that individual eukaryotic species segregate their chromosomes in one of two apparently different ways. Monocentric chromosomes attach to microtubules at a particular region (the centromere) and move toward the pole during anaphase with the centromere leading. In contrast, holocentric chromosomes bind to microtubules along their entire length and move broadside to the pole from the metaphase plate. Holocentric chromosomes are scattered throughout the plant and animal kingdoms, and may be products of convergent evolution. Alternatively, the ancestral eukaryotic chromosome may have been holocentric, in which case the restriction of kinetic activity to a specialized region must have been an evolutionary event that occurred again and again.
Perhaps because most laboratory organisms have monocentric chromosomes, holocentric species have been regarded with a mixture of curiosity and suspicion. These attitudes have begun to change precipitously due to...
