Evolution, 4th Edition

EvoluTion And dEvEloPmEnT 379

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_15.09.ai Date 02-08-2017

T2

lab Pb Dfd Scr

Antennapedia complex Bithorax complex

Antp Ubx abdA AbdB

A3

T1 A4

T3

A6 A7

A8

Sex combs reduced (Scr)

Antennapedia (Antp) Ultrabithorax (Ubx)

abdominal A (abdA)

labial (lab) Abdominal B (AbdB)

(^14131211109)
78
(^123456)
Deformed (Dfd)
A1A2
A5
FIGURE 15.9 Hox gene expression in Drosophila. At
center are schematics of the chromosome regions that
carry the Antennapedia and Bithorax gene complexes.
Regions where individual loci are expressed in the
embryo are shown in the schematics below, where
the intensity of shading corresponds to the expression
level. The corresponding tissues in the adult are shown
above. (After [14, 30].)
Futuyma Kirkpatrick Evolution, 4e
Sinauer Associates
Troutt Visual Services
Evolution4e_15.10.ai Date 11-02-2016
(A)
(B) (D)
(C)
FIGURE 15.10 Example of a developmental network: a simpli-
fied model of anterior-posterior pattern formation in the Dro-
sophila embryo. Anterior is to the left, and we view the left side
of the embryo. Colors show concentrations of protein products.
(A) Polarity is first established by maternal effect genes (e.g.,
bicoid, yellow to red) that leave protein concentration gradients
in the egg. These proteins are transcription factors that activate
expression of (B) gap genes such as hunchback (orange) and
Krüppel (green), which define broad territories in the embryo.
The gap gene transcription proteins determine the expression of
(C) pair-rule genes such as ftz, each of which specifies a region
about two segments long. Later in development, the pair-rule
genes activate (D) segment polarity genes such as engrailed
that divide each of these regions into two segment-sized units,
each with anterior-posterior polarity. These several groups of
genes determine the region where each homeotic selector (Hox)
gene is transcribed. These define the identity of each segment,
and initiate developmental pathways that result in the segment’s
various features. (A courtesy of C. Nüsslein-Volhard; B courtesy of
C. Rushlow and M. Levine; C courtesy of D. W. Knowles and the
Berkeley Drosophila Transcription Network Project, http://bdtnp.
lbl.gov/Fly-Net; D courtesy of S. Carroll and S. Paddock.)
15_EVOL4E_CH15.indd 379 3/22/17 1:30 PM