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Arabidopsis flower
sepal
stamen
carpel
petal
1
23
4
5
6
7 8
9
10
12
13
11
*
1 2 3 4
sepal petal stamencarpel
1 2 3 4A A
1 2 3 4B B
1 2 3 4C C
B
A C C A
B
carp
el
pet
al
pet
al
stam
en
stam
en
sep
al
sep
al
1 12 23 34
A = sepals
A + B = petals
C = carpels
B + C = stamens
Bowman and Meyerowitz, 1991
ABC Model
normal flower
B B
C C C C
B
normal A mutant
stam
en
stam
en
stam
en
stam
en
carp
el
carp
el
sep
al
sep
al
carp
el
carp
el
B
A C C A
pet
al
pet
al
stam
en
stam
en
A mutant
sepals are replaced by carpels
B
A C C A
B
normal B mutant
A C C A
sep
al
sep
al
pet
al
pet
alst
amen
stam
en
carp
el
sep
al
sep
al
sep
al
sep
al
carp
el
carp
el
carp
el
B mutant
petals arereplacedby sepals
B
A C C A
B
normal C mutant
B
A A A A
Bsep
al
sep
al
pet
al
pet
alst
amen
stam
en
carp
el
sep
al
sep
al
pet
al
pet
alp
etal
pet
al
*
C mutant
stamens arereplaced by
petals
C mutant
carpels arereplaced bya new flower
normal BC mutantse
pal
sep
al
pet
al
pet
alst
amen
stam
en
carp
el
BB
A C C A
A A A A
sep
al
sep
al
sep
al
sep
alse
pal
sep
al
*
BC double mutant
all organsare sepals
normal ABC mutantse
pal
sep
al
pet
al
pet
alst
amen
stam
en
carp
el
BB
A C C A
leaf
leaf
leaf
leaf
leaf
leaf*
ABC triple mutant
all organsare leaves
“Flower organs are modified leaves.”
Goethe, 1790
The C gene is active in cells that will form stamens and carpels
petal
sepalcarpel
leaf
sepalstamen
What would happen if the C gene was mis-expressedin cells that would normally form sepals?
petal
sepalcarpel
leaf
sepalstamen
ON/OFFstamens and carpels
C GENECODING REGION
sepalsadd sepal on/off switch:
remove on/off switch:
B
normal
stam
en
stam
en
carp
el
sep
al
sep
al
B
A C C A
pet
al
pet
al
Ectopic B activity
A C C A
B B
stam
en
stam
en
sep
al
sep
al
pet
al
pet
al
stam
en
Ectopic B activity
pet
al
pet
al
pet
al
pet
alst
amen
stam
enst
amen
A C C A
BB
Ectopic Bactivity
Ectopic B and C activity
stam
en
stam
en
stam
en
stam
enst
amen
stam
enst
amen
BB
C C
Ectopic B and C activity
Ectopic A and B activityin C mutant
pet
al
pet
al
pet
al
pet
alp
etal
pet
al *
BB
AA
Ectopic A and B activity in a C mutant
apetala1 mutant
B mutant
petals arereplacedby sepals
A mutant
sepals are replaced by carpels
