Mitotic recombination in the<i>paba 1</i>cistron of<i>Aspergillus nidulans</i>

The results of the analysis of 393 mitotic recombinants within thepaba1region ofAspergillus nidulanscan be summarized as follows:1. Reciprocal, non-reciprocal and probably inexactly reciprocal exchanges occur in intra-cistron mitotic recombination.2. Negative interference observed in intra-cistron mitotic recombination in thepaba1region ofAspergillus nidulansis more intense than that observed in meiotic recombination in the same cistron.3. In intragenic mitotic recombination multiple exchanges can involve three or even four chromatids within one effective pairing segment.</jats:p

Polarized negative interference in the<i>paba 1</i>region of<i>Aspergillus nidulans</i>

The intensity of negative interference in 28 crosses involving 14 allelicpabamutants in different combinations has been measured. Among selected cross-overs between two such mutants, when the distance between the mutants is large, additional exchanges on the distal side (relative to the centromere) greatly exceed those on the proximal side. With decreasing length of the interval of selection, the inequality disappears. It is suggested that this polarity may be the outcome of a undirectional process which imposes a time sequence on the recombination events within an effectively paired segment. Some alternative explanations of this result are discussed.</jats:p