The only rule in biology is that there are exceptions to every rule. This is what makes biology infinitely exciting; even when you think you’ve got the complete view, the floor can drop out from underneath you at any given moment. Case-in-point: The nucleus is the thing that makes eukaryotes...well, eukaryotes. It's the part of the cell that stores the genome, separating DNA from the cytoplasm and other organelles. (Bacteria do not have nuclei.) For decades, scientists thought that each nucleus contains one or more haploid sets of chromosomes. But there are exceptions. Red blood cells, for example, don’t have nuclei at all. (They expel their nuclei during maturation to maximize hemoglobin concentrations.) Cells in the eye lens, too, lose their nuclei and organelles during differentiation, thus becoming transparent. And so on. But now there is yet ANOTHER exception to this rule, and it’s one I hadn’t seen before. For a study in Science, researchers discovered that two types of pathogenic fungi that infect plants, called Sclerotinia sclerotiorum and Botrytis cinerea, have two different nuclei. And instead of storing a full set of chromosomes in each nuclei, they instead “distribute their chromosomes such that each of their nuclei contains only a subset of the haploid chromosomes.” The authors confirmed this by throwing a kitchen sink of methods at these cells; chromosome counting, DNA measurements using flow cytometry, single-nucleus PCR, and more. Nobody knows why the fungi do this, but the scientists claim (in their discussion) that it could enable them "to respond and adapt more effectively to local environmental stresses within their extensive mycelial networks. Nuclear shuffling may facilitate the rapid generation of new genotypes, enhancing adaptability to changing environments.” There is also evidence that the chromosomes within each nucleus may briefly collide during cell division, before going back into their separate nuclei. This is a great paper. It is simple, to the point, and challenges the status quo. It has serious potential to become a “classic” of the genre. Link: science.org/doi/10.1126/scie…