Pulsed-field gel electrophoresis and a chromosome-specific cosmid DNA library were used to determine the karyotypes of wild-type Aspergillus nidulans isolates from around the world. Overall, little structural variation was found, with a few major exceptions. One isolate possessed a non-essential B-chromosome of about 1.0 million base pairs (mb). Another isolate had undergone a non-reciprocal translocation of about 1.6 mb of chromosome VI onto chromosome VIII. Other than these chromosomal differences, these isolates appeared phenotypically normal. To analyze its effects on meiosis, the translocation isolate was outcrossed with another wild-type derivative that had a 'normal' electrophoretic karyotype. This cross produced a range of phenotypes, including duplicated progeny that had a 'barren' phenotype similar to that described for Neurospora partial disomics. The duplication was somewhat vegetatively unstable. This is the first association of sterility with chromosomal duplication in A. nidulans.
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