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New Experiences with Oenothera Mut. Pollicata
George H. Shull
The American Naturalist
Vol. 71, No. 732 (Jan. - Feb., 1937), pp. 69-82
Stable URL: http://www.jstor.org/stable/2457244
Page Count: 14
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(1) Oenothera mut. pollicata, which is distinguished by a solid hypanthium intervening between the distal end of the ovary and the proximal end of the style, recurred unexpectedly in 1934 in eight different families. Five of these families were from Lamarckiana-like parents and three from erythrina-like parents. (2) The distribution with respect to other segregating traits showed that mut. pollicata is independent of genes of the third linkage group and closely linked with genes of the first linkage group. (3) The presence of the well-known zygote lethals in the first linkage group conditions the manifestation of pollicata just as it does that of other first-linkage-group recessives. In progenies from selfed heterozygotes of Lamarckiana type, pollicata can appear only as the result of a transfer from the gaudens to the velans complex or vice versa. In the five progenies here reported from Lamarckiana parents, there were 466 non-pollicata and 7 pollicata, indicating a frequency of crossing over of the general order of 1.5 per cent. (4) In three families from erythrina-like parents, there was the usual segregation of erythrina and decipiens, in which all decipiens plants were pollicata, and all but one of the erythrina-like segregates had normal tubular hypanthia. In these three families there was a total of 403 plants, only one of which could be recognized certainly as a crossover, thus suggesting a crossover ratio of the general order of 0.25 per cent. (or of 0.5 per cent. if a narrow-leafed pollicata mutant be also assumed to have resulted from crossing over). (5) The occurrence of these new examples of mut. pollicata is supposed to be due to the unsuspected presence of the pollicata gene, generally, in those families which were derived from a common pair of ancestors in the cultures of 1928, but it is more difficult to believe they could have escaped detection through the fourteen generations required to connect all these families. It is deemed more probable that the pollicata gene-mutation has been repeated. (6) The pollicata gene removes an inhibition of growth at the top of the ovary in a narrow concentric ring separating the proximal portion of the style from the proximal portion of the hypanthium. It also diminishes the longitudinal growth of the hypanthium relative to that of ovary and bud-cone, and modifies the differentiation of mechanical tissue in the style. (7) The interpolation of a solid stem-like structure between the distal end of the ovary and the proximal end of the style as the result of a gene mutation makes easier an understanding of the manner in which different genera, families, orders, etc., may have originated.
The American Naturalist © 1937 The University of Chicago Press