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Unformatted text preview: ammals. Gilbert 9e, Fig. 19.8 Heterochrony in ﬂipper development of the
spotted dolphin may explain hyperphalangy Gilbert 9e, Fig. 19.8 Heterochrony is the phenomenon of expression of genes (or
productino of a cell/tissue) at a different time in different species.
Persistence of the AER’s signaling activity for a longer period of
time may explain hyperphalangy. Snakes show differences in
hindlimb AER vs. tetrapods
Modern snakes don’t
have forelimbs. Some
constrictors such as
pythons, boas, etc.)
do have rudimentary
about their AERs? Cohn and Tickle (1999). Nature 399, 474-479. Snake hindlimb AERs degenerate
after a limb bud forms
no AER The hindlimb AERs of modern snakes degenerate and cease FGF
production after a rudimentary limb bud forms.
Cohn and Tickle (1999). Nature 399, 474-479....
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