| Topic: |
Religions > Atheism |
| User: |
"Budikka666" |
| Date: |
23 May 2006 10:03:53 PM |
| Object: |
Yes, Whales Did Macro-Evolve |
http://scienceblogs.com/strangerfruit/2006/05/sonic_hedgehog_and_whales.php
"The main players in limb formation, the genes Sonic hedgehog (Shh),
the Fgfs, and the transcription factor Hand2, are all still present and
fully functional in these animals. What has happened, though, is that
there have been novel changes to their regulation. Even loss of
structures is a consequence of changes and additions to regulatory
pathways."
http://scienceblogs.com/pharyngula/2006/05/no_genes_were_lost_in_the_maki.php
Abstract of soon-to-be-published science paper:
"Among mammals, modern cetaceans (whales, dolphins, and porpoises) are
unusual in the absence of hind limbs. However, cetacean embryos do
initiate hind-limb bud development. In dolphins, the bud arrests and
degenerates around the fifth gestational week. Initial limb outgrowth
in amniotes is maintained by two signaling centers, the apical
ectodermal ridge (AER) and the zone of polarizing activity (ZPA). Our
data indicate that the cetacean hind-limb bud forms an AER and that
this structure expresses Fgf8 initially, but that neither the AER nor
Fgf8 expression is maintained. Moreover, Sonic hedgehog (Shh), which
mediates the signaling activity of the ZPA, is absent from the dolphin
hind-limb bud. We find that failure to establish a ZPA is associated
with the absence of Hand2, an upstream regulator of Shh. Interpreting
our results in the context of both the cetacean fossil record and the
known functions of Shh suggests that reduction of Shh expression may
have occurred ~41 million years ago and led to the loss of distal limb
elements. The total loss of Shh expression may account for the further
loss of hind-limb elements that occurred near the origin of the modern
suborders of cetaceans ~34 million years ago. Integration of
paleontological and developmental data suggests that hind-limb size was
reduced by gradually operating microevolutionary changes. Long after
locomotor function was totally lost, modulation of developmental
control genes eliminated most of the hind-limb skeleton. Hence,
macroevolutionary changes in gene expression did not drive the initial
reduction in hind-limb size."
Budikka
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