Futuyma Kirkpatrick Evolution, 4e
Sinauer Associates
Troutt Visual Services
Evolution4e_15.12.ai Date 12-14-2016(A)Pectoral ns onlyCo-option of Hoxa
genes in autopod
(novel enhancer)Co-option of posterior Hoxa
genes (9–13), expressed
in both appendages
Vertebrates
(paired
appendages)Two sets of paired
appendages
(serial homology)Tetrapods
(evolution of
autopod)Hoxa genes 1–13 expressed
along body axisPosition(B)
HindlimbHox gene expression Resulting Structures
ForelimbH FR TMC MT
Functional modules
HoxDevelopmental modulesProximalDistalForelimb91011 1312Hindlimb910 1211 13FIGURE 15.12 Co-option of developmen-
tal pathways in the evolution of novelties.
(A) Co-option of the vertebrate Hoxa genes
during evolution of the tetrapod limb.
Ancestrally, Hox genes were expressed
only along the anterior-posterior axis of the
developing body. The evolution of paired
forelimbs and hindlimbs involved novel
gene expression, presumably using novel
enhancer sequences of Hoxa genes 9–13.
Autopod refers to the wrist, ankle, and
digital bones. (B) The pattern of expression
of the Hoxa genes in the three regions of
the limb (developmental modules) is the
same in fore- and hindlimbs, which perform
different functions and are referred to as
functional modules. Bone names are H,
humerus; F, femur; R, radius; T, tibia; MC,
metacarpals; and MT, metatarsals. (A from
[78]; B from [87].)Futuyma Kirkpatrick Evolution, 4e
Sinauer Associates
Troutt Visual Services
Evolution4e_15.13.ai Date 12-14-2016(A) (B)FIGURE 15.13 (A) The fruit of a tomato plant
shows the sepals as small structures at the base
of the fruit. This is the condition in most mem-
bers of the plant family Solanaceae. (B) In the
ground cherry genus, Physalis, a gene that is
ordinarily expressed only in vegetative tissues is
transcribed in the sepals after the fruit starts to
develop. The sepals form the “Chinese lantern”
that envelops and protects the fruit.15_EVOL4E_CH15.indd 381 3/22/17 1:30 PM