On the Fertility Effects of Pericentric Inversions

I N the most extensive and thorough study of the fertil- ity of Drosophila females heterozygous for pericentric inversions carried out so far, COYNE et al. (1991, 1993) come to two important conclusions: (1 ) that many inversions do not show the expected degree of semisterility and are barely underdominant; and ( 2 ) that the degree of semisterility of inversion heterokaryotypes depends far more on the position of breakpoints than on the inversion length. These conclusions are surprising because one half of the chromatids produced by single or multiple crossovers within the limits of a pericentric inversion carry deficiencies and duplications and may end up in the functional gametes ( STUR-

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