from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. exhibiting metamerism
- adj. (chemistry) exhibiting structural isomerism
from the GNU version of the Collaborative International Dictionary of English
- adj. Having the same molecular formula, but possessing a different bonding structure and different properties. See isomeric.
- adj. Of or pertaining to a metamere or its formation.
from The Century Dictionary and Cyclopedia
- In chem., pertaining to or characterized by metamerism.
- In zoology, of or pertaining to a metamere or metamerism; being a metamere, or resulting from metamerism; situated in the long axis of the body as one of a longitudinal series of like parts; segmental; somitic.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- adj. having the body divided into successive metameres or segments, as in earthworms or lobsters
Sorry, no etymologies found.
We also see in various organs of the rabbit, and especially in the case of the limbs and vertebral column, what is called metameric segmentation, that is, a repetition of parts, one behind the other, along the axis of the body.
If I were a FLID supporter, I would propose that the homeobox regulatory mechanism for body regions was a "front-loaded design element" that, once it was in place, could be modified extensively via standard evolutionary mechanisms to produce the various metameric metazoan bauplans.
All we know is that all of the known metameric animals use essentially the same mechanism to regulate the development of their multiple body segments.
In Gould's concept of the term, the original homeobox regulatory mechanism would have evolved first in non-metameric animals, and then become modified later in the dominant metameric forms (i.e. arthropods and vertebrates).
Furthermore, this regulatory mechanism almost certainly evolved among organisms that were not metameric, but then became modified later in those descendant lines that became metameric.
As far as we know, all metameric organisms use the same underlying genetic regulatory mechanism to produce segmented (i.e. metameric) bodies.
As an evolutionary biologist, I would assert that the modification of the ancestral homeobox function (i.e. longitudinal differentiation) into the regulation of longitudinal metameric development would qualify as an example of evolutionary exaptation, which Stephen Jay Gould emphasized as one of the principle mechanisms of macroevolution.
In the context of this thread, the homeobox regulatory mechanism of non-metameric ancestral metazoans (such as flatworms) would qualify as an exaptation for the homeobox regulatory mechanism of their metameric descendants.
The earliest metameric pattern, that of the pair rule genes, has 7 stripes that are determined one by one by the action and interaction of a particular combination of gap gene products (32, 33).
The failure to find mutations resembling the gap and pair rule mutations in the fish may mean that the formation of metameric patterns differs between Drosophila and most other animals.
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