Figure 6.—

Tests for silencing transmission of oocytes and linkage to the chromosomal locus exposed to dsRNA. (A) Schematic of crosses designed to follow chromosome origin from oocyte transmission. We injected animals that were morphologically dumpy by carrying a homozygous recessive allele of dpy-20(e1282ts). The dpy-20 allele is linked to the oma-1 locus and marks the origin of the chromosome. Injected animals self-fertilized and we used the F₁ hermaphrodites to cross with males not exposed to dsRNA and with a wild-type copy of the dpy-20 gene. The cross-progeny were non-dumpy heterozygous (only cross-progeny are non-dumpy). We then allowed heterozygous animals to produce self-fertilized progeny. Dumpy animals are dpy-20(e1282ts) homozygous and non-dumpy animals are either homozygous wild type or heterozygous for dpy-20(e1282ts). F₃ animals descended from F₂ cross-progeny inherited chromosomes from ancestors exposed or not exposed to dsRNA. We scored the F₃ animal's capacity for producing viable progeny. (B) Results of linked heritable silencing assay. We followed the genetic scheme described in A and individually plated F₃ animals carrying exposed or nonexposed chromosomes to dsRNA. Homozygous animals carrying the wild-type dpy-20 allele inherited their oma-1 locus from nonexposed animals. To determine if silencing was segregating with the origin of the chromosomes, we used animals having broods of >10 progeny. We used two ranges in brood size (10–30, open bars; >31, shaded bars) as indicators of the efficacy of the silencing achieved. Error bars are 1 SD. The silencing efficacy of F₃ animals demonstrates that (1) the transmission through the oocyte is sufficient to transmit silencing capacity and (2) the silencing capacity is unlinked to the origin of the oma-1 locus.