Quantifying Embryonic Lethality Rate in Caenorhabditis elegans

Embryonic lethality is a cornerstone phenotype used in Caenorhabditis elegans research to characterize developmental defects arising from factors such as toxic exposures and genetic mutations. Therefore, accurately quantifying the penetrance of embryonic lethality is critical for understanding the mechanisms and impact of these perturbations on animal development. Although automated scoring platforms exist, these approaches often require substantial financial investment and specialized hardware or software. This article describes a low-tech, low-cost assay that quantifies embryonic lethality by measuring the percentage of embryos that successfully fail to hatch. Notably, this version of the assay eliminates the need for a worm pick, making it exceptionally suitable for beginners. An additional advantage of this approach is that each technical replicate assays progeny from multiple animals, avoiding the potential biases of single-worm assays. This protocol includes a discussion of critical parameters, such as the minimum number of progeny required to accurately capture phenotype penetrance and the rationale for the methodology. Finally, we provide guidance on adapting the assay to assess the effects of gene knockdown via RNA interference, pharmacological treatments, or nutritional supplementation, adding a versatile and accessible tool to the toolkit of C. elegans researchers.