Three experiments were performed in different years to study a pleiotropic effect of two marker genes A and B on quantitative traits in Arabidopsis thaliana L. (Heynh.) Experiments differed in their conditions for plant growth (light intensity and soil fertility). In experiment 1, substitution of B- by bb did not affect the duration of the sowing-flowering period, whereas substitution of A- by aa caused a 2-day delay in flowering. Experiment 2 showed that both genes affected this trait. The delay in flowering was one, two, or three days when B- was substituted by bb, A- by aa, or A-B- by aabb, respectively. Therefore, these genes were additive. Data of experiments 3 were opposite to those of experiment 1: substitution of A- by aa did not affect the trait studied, whereas substitution of B- by bb caused a 2-day elongation of the sowing-flowering period. Thus, variations in growth conditions transformed the effects of the marker genes duration of the sowing-flowering period and changed a set of genes that determined this trait. Note that effects of A and B genes on other qualitative and quantitative traits (for example, plant height) were constant in all experiments. Therefore, transformation of a gene set, which influenced the sowing-flowering period, was not related to the repression or derepression of A and B genes.
