1. FORMING THE NOSE VERSUS TAIL OF A FLY
LECTURE 6:
FORMING THE NOSE VERSUS TAIL OF A FLY

2. The Body Plan of a Fly MaggotV
Head
Thorax
Abdomen
Tail
“Denticle” Hairs
Skin
Nervous System
(inside)

3. Fly Embryonic Patterning Mutants
Anterior-Posterior Patterning Mutants
Dorsal-Ventral Patterning Mutants

4. Hierarchy of Gene Action in A/P Patterning
Bicoid
Controlled
by Mother A P
Gap Genes
Controlled
by Embryo
Kruppel
Pair-rule Genes
even-skipped
Segment Polarity Genes
(e.g., engrailed)
Homeotic Genes
(e.g., Bithorax)

5. Bicoid A P
Hunchback
Even-skipped 1 2 6 5 3 4 7
Knirps
Homeotic

7. Independent Regulatory Elements Activate
even-skipped Expression in Different Stripes 7 1 2 3 4 5 6
even-skipped
stripes On
Off
OtherStripes
Coding Region
Regulatory Region
even-skipped
mRNA
Stripe 2
Stripe 3

8. Condition for Activating Expression of even-skipped Stripe 3
1. An activator, which is expressed everywhere, must be present.
2. Repressors, Hunchback and Knirps, must be absent. Hb
Kni 3
even-skipped
stripe 3

9. Dorsal-Ventral Patterning Mutants

10. Hierarchy of Gene Action in D/V Patterning
High [Dorsal]
Low [Dorsal]
No Dorsal
Graded Dorsal Concentration
Created by Mother
Mesoderm Genes
Neuronal Genes
Epidermal Genes
D/V Genes
Basic Tissue Types
Controlled by Embryo D V

11. Ventral Epidermal Genes Neural Genes
Dpp
Neuronal Genes
Brk, Sog
Dorsal Genes
AS-C
Rho
Ventral Epidermal Genes
Neural Genes
Snail
Neural Genes
Twist
Mesodermal Genes = M e s o d r m N n - u a l E c t