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# Tetrad Analysis in Fungi ## Neurospora crassa **Description of the Organism:** It is a bread mold. The fungal mat or mycelium (mycelia, plural) is composed of intertwined filaments called hyphae. The tips of hyphae (hypha, singular) may pinch off asexual spores called conidia (conidium, singu...

# Tetrad Analysis in Fungi ## Neurospora crassa **Description of the Organism:** It is a bread mold. The fungal mat or mycelium (mycelia, plural) is composed of intertwined filaments called hyphae. The tips of hyphae (hypha, singular) may pinch off asexual spores called conidia (conidium, singular), which germinate into more hyphae. Vegetative hyphae are segmented, with several haploid nuclei in each segment. Hyphae from one mycelium may anastomose with hyphae of another mycelium to form a mixture of nuclei in a common cytoplasm called a heterokaryon. **Sexual Reproduction:** A pair of alleles, A and a, governs the two mating types. Sexual reproduction occurs only when cells of opposite mating types unite. Specialized regions of the mycelium produce immature female fruiting bodies (protoperithecia) from which extrude receptive filaments called trichogynes. A conidium or hypha from the opposite mating type fuses with the trichogyne, undergoes several karyokineses, and fertilizes many female nuclei. Each of the resulting diploid zygotes lies within an elongated sac called the ascus. The zygote divides by meiosis to form four nuclei, followed by a mitotic division that yields four pairs of nuclei, maturing into eight ascospores. A mature fruiting body (perithecium) may contain over 100 ascospores. **Diagram Description:** The diagram (Fig. 6-5. Life cycle of Neurospora crassa) illustrates the life cycle of *Neurospora crassa*, showing both sexual and asexual reproduction. It shows the stages of the cycle, starting with a germinating conidium or hypha, proceeding to the protoperithecium, into the formation of mature asci, and finally producing germinating ascospores. The diagram includes labeling for different structures in the cycle such as conidia, protoperithecium, mature ascus, and perithecium. It clearly depicts the process of the transition from asexual to sexual reproduction, and the resultant formation of ascospores.