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| Modern Genetic Analysis Chapter 4. The Inheritance of Genes Inheritance Patterns of Individual Genes Figure 4-11. Certain fungi provide excellent systems for the study of allele segregation at meiosis. (a) In the fungus Neurospora (pink bread mold), meiosis produces four product nuclei (the tetrad), which then undergo mitosis to produce an octad. Since the meiotic and mitotic nuclear divisions all occur in a long, thin cell, nuclei never slip past each other, so the products form an ordered linear array. (b) An A/a meiocyte undergoes meiosis (and afterwards, mitosis), resulting in equal numbers of A and a products, a direct demonstration of the principle of equal segregation of alleles at meiosis (Mendel's first law). (Note: the meiosis illustrated happens to have no crossover in the region between the centromere and the gene under study. A crossover here would change the pattern of ascospores in the ascus but would not affect the 1:1 ratio of alleles in the meiotic products.)

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