VII. Chromosome linkage in certain oenothera hybrids

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Abstract
The genetical peculiarities of the genus Oenothera have long been recognized, but further work will, no doubt, reveal similar conditions in other groups. The immense amount of genetical work done with the Oenotheras by de Vries (1913) and many others lias given a body of data unequalled in any other group of plants. Every phase of the life history lias been intensively investigated (see Gates, 1928) and the results of great numbers of species- and variety-crosses are known. Two of the most striking peculiarities discovered by de Vries (1907) and confirmed by others (Gates, 1913) were (1) the occurrence of twin types in the F 1 of crosses between different species, and (2) the fact that many of the F 1 forms produced by crossing breed true or segregate in only one or two characters. By crossing, numbers of Oenothera species have been analyzed, particularly by Renner (1925), into two “complexes,” both of which may be active in different egg cells of the plant, but frequently only one of them is functional in the pollen. The basis of this failure of Oenothera hybrids to segregate in Mendelian fashion has long been obscure, but it is now becoming clear that it has a cytological basis in the linkage of the chromosomes during meiosis, which is a common feature of Oenothera species, mutations, and hybrids. It is only necessary here to mention that each species has its characteristic linkage arrangements, and that fresh linkages different from those of the parents occur in the mutations of Oe. Lamarckiana and also in hybrids between different species. It is to be anticipated that the more numerous such chromosome linkages are, the smaller will be the amount of ordinary Mendelian free assortment of factors.