Figure 9.—

Explicit test of male transmission of silencing. (A) Males during copulation transmit both sperm and seminal fluid. The male-derived silencing efficacy can be explained by at least two models: (1) The silencing factor is inside the sperm and (2) the silencing factor is transmitted through the male in the seminal fluid. (B) Schematic of crosses designed to test the male transmission of silencing through the sperm or the seminal fluid. It was critical for this experiment that we identify self-progeny animals that had been fertilized after their parent hermaphrodite had received male sperm and seminal fluid. To ensure this, we transferred the parent hermaphrodites each day and scored only self-progeny that derive from mothers that had previously produced cross-progeny. Operationally, this was carried out by mating individual F₁ male silencing carriers with five naive hermaphrodites for 6–12 hr, transferring the hermaphrodites to individual fresh plates to allow egg laying for 1 day (first brood), and transferring hermaphrodite mothers to a second plate for an additional day (second brood). Of 50 mated hermaphrodites, 6 met the criterion that they had some cross-progeny on the first day of transfer and some self-progeny on the second day of transfer. The self-progeny broods on these six plates from the second transfer consist of self- and cross-progeny that were fertilized subsequent to the transfer of sperm and seminal fluid from males to the mother hermaphrodite. We then compare silencing transmission to self-progeny and cross-progeny from these broods. The boxes summarize the viability of F₃ and F₄ cross- and self-progeny from first and second transfers at 25°. The data show that carrier males transfer the silencing trait to cross-progeny and not to self-progeny. This is consistent with a signal intrinsic to sperm and not one carried in the seminal fluid. The asterisk indicates that a single viable F₃ larva was produced from 1 of the 36 F₂ animals in this experiment; this animal yielded no F₄ progeny and may have represented a rare “spontaneous rescue” affecting ∼1 in 10⁴ progeny of oma-1(zu405) mothers.