Analysis of the Heritability of Cortical Inversions through Sexual Exchange in Paramecium tetraurelia
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Paramecium tetraurelia is a large, single-celled, ciliated protist. Short cell cycle times (4.5-5 hours) and manipulable Mendelian genetics have made it an attractive research species, particularly for developmental genetics investigations. A genetic cross between cells with inverted ciliary rows and cells with normal cortexes was performed to determine the heritability of cortical inversions through sexual exchange in P. tetraurelia. A nuclear gene, nd6, which confers trichocyst nondischarge, was used in the cross to demonstrate a Mendelian inheritance pattern. Quantitative scoring of cortical phenotypes, including the location and size of the inversion, and the total number of ciliary rows was performed for the P1, F1, and F2 generations. The nd6 mutation was inherited in a typical Mendelian pattern. The inverted ciliary rows were inherited only through the progeny of the conjugant originally possessing the inversion and were not transferred to the other partner of the cross. Inheritance of the cortical inversion was stable in each generation; in no instances did F1 and F2 lines with inverted rows spontaneously lose them, nor did F1 and F2 lines with normal cortexes spontaneously generate inverted cortical rows. These results demonstrate that cortical units follow a non-Mendelian inheritance pattern that is consistent with the phenomenon of structural inheritance, or directed assembly.
Cross, Rebecca (2012). Analysis of the Heritability of Cortical Inversions through Sexual Exchange in Paramecium tetraurelia. Honors and Undergraduate Research. Available electronically from