"OLD-GOLD" FLOWER COLOR, THE SECOND CASE OF INDEPENDENT INHERITANCE IN OENOTHERA

Abstract

The independence of the factor pair Vv, which differentiates between yellow and old-gold flower color, from the lethals and from the factor pair Br br, which differentiates between long styles and short styles, is demonstrated by extensive tests, the tables containing the results of sowing more than 69,000 seed in about 280 pedigree families. The factor v is recessive to its normal allelomorph V and segregates out of crosses with yellow-flowered O. lamarckiana, in the F2 and later generations only, and approximately in the typical monohybrid Mendelian ratio. " The dominant factor V is complementary to the factor S, the normal allelomorph of the factor s characteristic of sulphur-colored flowers; the F1 hybrids between old-gold and sulphur are always yellow. Yellow-flowered plants heterozygous for both old-gold and sulphur, self-fertilized, segregate in a dihybrid ratio which is the typical 93:3:1 when the sulphur factor is not accompanied by a lethal factor, the double recessive ss vv being a 4th flower-color type, called "gold-center." Tests of yellow-flowered segregates in the F2 following self-fertilization showed them to consist of homozygous and heterozygous yellows in the typical ratio 1:2, and a similar test of the yellow-flowered plants in a family that split 9:3:3:1 showed the typical Mendelian distribution into 1:2:2:4 of homozygotes and heterozygotes. These ratios show the independence of old-gold from sulphur and from the lethal factors of the 1st linkage group. Data are presented which also demonstrate its independence from rubricalyx bud color, and nanella stature, other group I factors. Since the factor v is independent of the factors of linkage group I, and also independent of brevistylis in linkage group II, it becomes the 1st factor of a new linkage group III. A 2nd factor, sp (mut. supplena), in this 3rd linkage group has also been announced. The author discusses the bearing of these new discoveries on the mechanism of linkage and crossing over in the Oenotheras, holding that the cohesion of non-homologous chromosomes to form circles (Cleland) is a scarcely adequate mechanism to meet the following observed genetical facts: (1) the number of known factors in linkage group I is about twice as great as the haploid number of chromosomes in Oenothera; (2) the amount of observed irregularity in the distribution of the chromosomes is greater than the percentage of crossing over would require; (3) the 15-chromosome mutants show that each chromosome has specific effects on nearly all parts of the plant, while the crossover individuals show no disturbance of the general characteristics of the plants; (4) O. lamarckiana has only 1 pair of chromosomes free from the big chromosome circle, but can have 2 independently segregating factors, brevistylis and old-gold; (5) different forms having different numbers of chromosomes involved in the circle should exhibit dissimilarity in the number of linkage groups present, but no such differences have yet been found. Admittedly, however, such differences may be found.