lecture 8. Epistasis and Pathways

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

3 Y Z 1 X X Y 1 2 Z X Y 1 2 3 Z

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

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

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°

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

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

OFF ON ON OFF

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

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