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Science 5 October 2001:
Vol. 294. no. 5540, p. 9
DOI: 10.1126/science.294.5540.9m
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Toxoplasma, which undergoes sexual reproduction and might be expected to show a high degree of genetic mixing among strains, exists as only a few genetically distinct "clonal types." Grigg et al. (p. 161) analyzed polymorphic loci and found that the three major types originated from rare crossing events between two ancestors. Such reassortment may have been crucial in the development of virulence, as a cross between two avirulent strains resulted in an organism that was highly virulent in mice. Virulence is likely to be attributable to a combination of factors rather than a single gene.




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Science. ISSN 0036-8075 (print), 1095-9203 (online)