Summary
Mapping within the am gene of Neurospora crassa is possible only because of a marked polarity of conversion within the gene, seen in the unequal frequencies of the two parental flanking marker combinations among the selected intragenic recombinants. The conventional comparison of the frequencies of the two flanking marker recombinant classes gives only uncertain and conflicting indications of the orientation of sites within the gene. While other possible interpretations are not ruled out, it is suggested that one relatively simple way of explaining the data is to suppose (a) that most recombination within am is due to conversion without immediately associated crossing-over, and (b) that recombinational events (conversions and cross-overs) tend to occur in tight clusters, so that conversion within the gene has a high probability (apparently about 25 per cent in am) of being accompanied by an independently initiated cross-over close by and on either side more or less indiscriminately.
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References
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Fincham, J. Negative interference and the use of flanking markers in fine-structure mapping in fungi. Heredity 33, 116–121 (1974). https://doi.org/10.1038/hdy.1974.75
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DOI: https://doi.org/10.1038/hdy.1974.75
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