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Mitosis

Ascus showing normal Mendelian segregation

FIGURE 14.28 Mendelian Ratios in Ascospore Formation

In certain fungi a structure known as an ascus keeps together groups of spores ("ascospores") derived from a single zygote. This allows the observation of Mendelian ratios from a single occurrence of meiosis.

Ascus showing normal Mendelian segregation

Ascus

Eight ascospores (n)

Ascus showing gene conversion

Ascus

Eight ascospores (n)

Ascus showing gene conversion oooooooo of four spores all derived from the same zygote (Fig. 14.28). Sometimes mitosis immediately follows meiosis and results in eight final spores. These four (or eight) "ascospores" all stay together inside a special bag-like structure, the ascus. It is thus possible to count the Mendelian ratio separately for each group of four (or eight) offspring derived from the same individual zygote.

ascus Specialized spore forming structure of ascomycete fungus

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