A Lethal for Ascus Abortion in Neurospora

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Abstract
SUMMARY A culture, G5–3, of Neurospora tetrasperma derived from a bisexual x-rayed ascospore is practically self-sterile, but it reacts sexually as sex A with tester strain S1. The resulting ascocarps contain numbers of dark-colored aborted indurated asci with no spores, as well as some asci that mature ascospores. Cultures obtained from bisexual f1, f2, f3 and f4 ascospores produce perithecia which in turn contain the dark-colored empty asci. The lethal for ascus abortion is segregated at meiosis so that each bisexual ascospore contains at its origin one normal and one deficient nucleus, that is, one containing the lethal agent, whatever it may be. The lethal for aborted ascus is, therefore, carried on from generation to generation only through those ascospores containing two nuclei of opposite sex at their origin. The small uninucleate, and therefore unisexual ascospores are of two sorts. Some die soon after they germinate. These carry the lethal. Others being normal produce mycelia of normal growth. Of the latter, two of opposite sex, when mated together, produce normal perithecia with no aborted indurated asci whatever.