3. lecture 8. Epistasis and Pathways

4. Interactions of null alleles
Additivity of nulls implies distinct pathways
Epistasis of nulls implies common pathway
Synergism of null alleles implies parallel pathways
with a common target
Additivity of hypomorphs is consistent with anything

5. 3 Y Z 1 X X Y 1 2 Z X Y 1 2 3 Z

7. A B Yes ON ON No OFF OFF outcome 1 condition outcome 2 outcome 1
Switch Regulation Pathway
outcome 1
condition A B
outcome 2
Yes ON ON
outcome 1 No
OFF
OFF
outcome 2

8. A B Yes OFF ON No ON OFF outcome 1 condition outcome 2 outcome 1
Switch Regulation Pathway
outcome 1
condition A B
outcome 2
Yes
OFF ON
outcome 1 No ON
OFF
outcome 2

10. Some C. elegans sexual specializations
Male tail
sensory structures
that locate the vulval
opening
spicules
Hermaphrodite vulva 2°
1°: the opening
vulval muscle-1 insertion
cues to male
2°: vulval muscle-2 insertion 1°

12. somatic sex determination in C. elegans
genotype XX XO
+ f m
tra-1(lf) m m
tra-1(gf) f f
her-1(lf) f f
her-1(gf) ~m m
f, female somatic tissues;
m, male somatic tissues.
lf, loss-of-function;
gf, gain-of-function

13. somatic sex determination in C. elegans
genotype XX XO
+ f m
tra-1(lf) m m
tra-1(gf) f f
her-1(lf) f f
her-1(gf) ~m m
tra-1(lf); her-1(lf) m m
tra-1(gf); her-1(gf) f f

14. OFF ON ON
OFF

17. x Intragenic revertant of a dominant mutagen egl-1(sd) + + ced-9(gf)
+ +
egl-1(sd) ced-9(gf+lf) x
Common
Non-Egl OR
Rare Egl
In egl-1(sd) mutants, the HSN dies, and hence the hemaphrodites cannot lay eggs

19. ced-3(lf) NO cell death
ced-4(lf) NO cell death
ced-1(lf), 2, etc No engulfment
ced-9(gf) NO cell death
ced-9(gf+lf) EXTRA cell death
nuc-1 No DNA degradation
ced-3(lf) ced-9(lf) NO cell death
ced-3 (lf) nuc-1(lf) NO cell death