Enhanced identification of lethal yellow (Ay/Ay) mouse embryos by means of delayed development of four-cell stages.

At present, experimental studies on the primary genetic lesion in Ay/Ay embryos are restricted by the absence of techniques designed to identify Ay homozygotes prior to the onset of secondary defects. This paper describes a methodology to enrich the yields of Ay homozygotes in experimental populations by taking advantage of an early homozygous Ay expression-lagging development in 4-cell embryos.