Renner's Studies on the Genetics of Oenothera

Abstract

Columbia University and Carnegie Institution of Washington T H HERE is only one group among the higher animals and plants that has persistently failed to give genetic results that can easily be interpreted by means of the generally applicable principles. The Evening Primrose (Oenothera) has been studied for thirty years, first by de Vries and more recently by a number of other workers; but the results obtained are still quite anomalous as compared with what is known of any other intensively studied organism. The cytological work of Miss Lutz, Gates, Stomps, Boedijn and others has now shown that many of the results are due to the occurrence of triploid, tetraploid, and trisomic (2n + i) types; but apart from variations in chromosome number there remains a mass of puzzling data as to the behavior of the I4-chromosome species and races. Oenothera Lamarckiana was long ago shown by de Vries to produce regularly about z per cent of offspring. About three fourths of these can now be identified as due to extra chromosomes; the remainder appear to be due to heterozygosis in the parent. But if Lamarckiana is regularly heterozygous, why does it not produce a still higher percentage of new types-at least z5 per cent-among its offspring? When Lamarckiana is crossed to other species of Oenothera, F1 usually includes two distinct ypes, though both parent species breed nearly trueand these themselves often breed nearly true. Many species crosses in Oenothera; give different results according to which species furnishes the egg, which the pollen. Finally, the ratios obtained from various mutant and species crosses in the group are variable and are rarely in accord with simple Mendelian expectations. These and other remarkable peculiarities of the Evening Primrose have been intensively studied in Germany by Professor Otto Renner, and it is the purpose of the present review to show how Renner's work helps to explain the genetic behavior of Oenothera. The first two papers to be considered (I9I4, I9I7a) deal with the problem of the twin hybrids produced by Lamarckiana. Renner found that when Lamarckiana is self-fertilized, about half the seeds formed are incapable of germination. But when Lamarckiana is fertilized by biennis or muricata (crosses which result in twin hybrids) practically all the seed is viable. Renner therefore assumed that Lamarckiana is heterozygous for two genecomplexes, neither of which is viable when homozygous. One of these, called gaudens, produces the twin known as laeta; the other, known as velans, produces the twin velutina. Lamarckiana is then gaudens-velans; the inviable seeds are gaudens-gaudens and velans-velans. The hypothesis accounts for several other facts, such as that Lamarckiana may be