Figure 1. The germline of C. elegans. After zygote formation, a series of unequal cleavages generates the germline cells P₁–P₄ and five somatic founder cells (AB, MS, E, C, D). During embryogenesis the primordial germ cell P₄ divides once into Z2 and Z3. During postembryonic development mitotic divisions generate more than 1000 germ cells. In the hermaphrodite they first differentiate into sperm and then into oocytes. Self-fertilization results in a new zygote as the starting point of the next generation.

Figure 2. The gonad of C. elegans. (a) Four-celled gonad primordium in the freshly hatched C. elegans juvenile. Z2 and Z3 are the daughters of the primordial germ cell P₄. They produce all gametes. Z1 and Z4 are descendants of the somatic founder cell MS. They give rise to gonadal sheath, spermatheca and distal tip cell. (b) Gonad of the adult C. elegans hermaphrodite. Yellow, proliferative (mitotic) phase; orange, germ cells arrested in meiotic prophase; purple, most mature oocyte has left meiotic prophase. In cleaving embryos, germline cells are marked in red. dtc, distal tip cell. (c) Gonad of adult C. elegans male. The single arm of the male gonad carries two distal tip cells. Colours separate different stages of germ cell development analogous to (a).

Figure 3. Sex determination in C. elegans. (a) General scheme for different pathways of dosage compensation and sex determination. (b) Cascade of negatively regulated gene activities for sex determination in the germ cells of hermaphrodites and males. After Hodgkin 1990.