Analysis of double-mutant phenotypes to find order of genes in developmental pathways

(a) In wild-type worms, the vulva developmental pathway is active only in the presence of the signal (LIN-3). (b) In lin-3 mutants, no signal is present, and worms develop with a vulva-less phenotype. (c) and (d) In either let-23 or let-60 gain-of-function alleles, the pathway is constitutively active, and worms develop with a multi-vulva phenotype. (e) and (f) Gain-of-function alleles of let-23 and let-60 are epistatic to loss-of-function lin-3 alleles. The pathway is constitutively active regardless of whether the lin-3 signal is present.(g) and (h) Gain-of-function alleles of let-60 are epistatic to loss-of-function alleles of let-23. Conversely, loss-of-function alleles of let-60 are epistatic to gain-of-function alleles of let-23. This places let-60 downstream of let-23(a) In wild-type worms, the vulva developmental pathway is active only in the presence of the signal (LIN-3). (b) In lin-3 mutants, no signal is present, and worms develop with a vulva-less phenotype. (c) and (d) In either let-23 or let-60 gain-of-function alleles, the pathway is constitutively active, and worms develop with a multi-vulva phenotype. (e) and (f) Gain-of-function alleles of let-23 and let-60 are epistatic to loss-of-function lin-3 alleles. The pathway is constitutively active regardless of whether the lin-3 signal is present.(g) and (h) Gain-of-function alleles of let-60 are epistatic to loss-of-function alleles of let-23. Conversely, loss-of-function alleles of let-60 are epistatic to gain-of-function alleles of let-23. This places let-60 downstream of let-23

(a) Wild type (b) [in-3 loss-of-function (or (c) let-23 gain-of—function (d) let-60 gain-of-function let-23 or let-60 loss-of-function) Normal Vulva-Iess Multi-vulva Multi-vulva (e) [in-3 loss-of-function (f) Iin-3 loss-of-function (g) let-23 Ioss-of-function (h) let-60 loss-of-function + + + + let-23 gain-of—function let-60 gain-of—function let-60 gain-of—function let-23 gain-of-function VPC Multi-vulva Multi-vulva Multi-vulva Vulva-less