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genes and embryos



Mickey P. Rowe wrote (re. color photoreceptors):
"It's also possible that some of us (humans) have four
(although the spectral sensitivity of the fourth is roughly identical
to that of one of the others since we are possibly in the incipient
stages of a gene duplication event -- Neitz, Neitz and Jacobs, 1993)."

My two (small) cents:  the idea that morphological complexity, innovation
of novel structures, or duplication of structural parts (as seems to be
implied above) is a direct result of gene or genome duplication is not
well-supported by the current data.  It is an idea, though, that has
become promoted almost to the status of 'fact' by folks like Peter Holland
and Frank Ruddle.  It looks like there was an *ancient* extra round of
polyploidization shared by the teleost fish (Postlethwait et al. 98) - and
while these fish are extremely speciose, it's not clear that they are
twice as morphologically complex as other vertebrates. ;)  The previous
ancient polyploidizations (totalling two rounds in most other vertebrates)
may or *may not* have coincided with the emergence of the vertebrates
and then gnathostomes - in fact, we just don't have it timed yet.  One or
more of these genome duplications could even have post-dated the seminal
innovations of the vertebrates (paired appendages, neural crest-derived
structures, etc)...
My apologies to Mickey Rowe if I've misinterpreted what he meant!!

On a totally different, and maybe a more relevant tack, does anyone out
there hold any hope of seeing fossil evidence of cartilage condensations
in embryonic dinosaurs?  Are people looking for that at all?  I mean the
condensations that presage bones in developing limbs, for example.  Too
much to ask for, huh?  OK.  (I'm thinking of the Burke and Feduccia paper
- Science 278. 1998).
Thanks!
Susie Bassham