Incorporation of 5-iododeoxyuridine into Dna of Plant Cells.

spora, provided a source of aneuploidy is present, we have interpreted the consistent failure to find evidence of somatic crossing over in heterokaryons to indicate that there is no source of aneuploidy present in these cultures. This suggests that fusion of nuclei of the same mating type within a heterokaryon to form diploid nuclei simply does not occur in heterothallic Neurospora. It is for this reason that we favor the hypothesis that it is somatic crossing over in the disomic nucleus that accounts for the results, rather than nuclear fusion within a heterokaryon to give a diploid followed by crossing over and haploidization.