gametophyte reduction

Dana Ann Dudle ddudle at steel.ucs.indiana.edu
Fri Oct 1 10:12:27 EST 1999


Hi All--

After such helpful and interesting responses to my question regarding
polyploidy, I have decided to try yet another question on y'all:

What were the intermediate steps between the dominant, photosynthetic
gametophyte and reduced sporophyte present in the non-vascular plants
(bryophytes), and the dominant sporophyte that is present in all vascular
plants (as far as I have been able to discern).  The oldest fossils of
vascular plants that are most often referenced in textbooks and review
articles, e.g. Cooksonia and Rhynia, are called sporophytes... 

IT seems as if this was a very important development in the evolution of
plants, and yet I have found very little reference as to HOW this change
occurred.  Does anyone know of fossil evidence or living transitional
forms that may give some insight into this major change in the focus of
the alternation- of- generations in land plants?

I have always been taught that "mosses have dominant gametophytes, and
ferns have dominant sporophytes", but I have not questioned the "how or
why" until I started writing lectures and preparing classes on this topic.

Any hints or leads would be greatly appreciated (as well as speculations!)

Thanks,
Dana
*********************************
Dana A. Dudle                   
Dept. of Biological Sciences
DePauw University
Greencastle, IN  46135
ddudle at depauw.edu
*********************************



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