Genetics of the soybean

1. A list of genes and a chromosome map are given to show the progress made to date in a genetic analysis of the soybean. 2. The mode of inheritance of three characters is described. Bloom on the seed coat is considered to be due to three complementary genes B1, B2, and B3, all three of which must be present to produce the character. Variegated leaf (v1) is a simple recessive to normal (V1), and determinate pod-bearing habit (dt) is a simple recessive to indeterminate habit, (Dt). 3. Data on the inheritance of hardness vs. softness of seed coat are presented. Ability to imbibe water readily appears to be partially dominant in the F1, and in F2 there is wide variation, a few segregates even transcending the limits of the parents, thus illustrating transgressive segregation. A relation to seed color was indicated, and the color genes involved in this relationship were thought to be R2T. 4. Hybrid vigor was illustrated in three crosses, in two of which one variety was a common parent. In one of these two crosses much more heterosis was evident than in the other. 5. An attempt was made to resolve seed yield into simpler components, to study each separately, and to compare varieties with respect to each. As a result of these studies a variety was thought of as a biotype, having its own complex of characters each expressed to a certain degree, the end result of which may be the same as for another variety, but attained in a different way. 6. Genetic correlations were calculated between the yield components and yield and between the components themselves. Little relationship was indicated between these and yield, though it appeared that varieties with high percentage of abortive seed and small seeds tend to be low yielders and varieties with low percentage of abortive seed and large seed tend to be high yielders. In general, the yield components showed no significant correlations with one another. However, it may be concluded that large-seeded varieties tend to have a high number of nodes and a low percentage of abortive seed.