GENETIC DETERMINATION OF ISOZYME VARIATION IN THE BLADDER CAMPIONS, SILENE-UNIFLORA AND S-VULGARIS

The genetic control of variation at the Pgi-2, Pgm-1, Pgm-2, and Tpi-1 loci was investigated for the gynodioecious bladder campions, Silene uniflora and S. vulgaris. The main objective of the study was to deter mine whether alleles 1 and 2 at Pgi-2, which have closely similar elec trophoretic mobilities, were genuine Mendelian alleles. The results fr om a series of crossing experiments were consistent with a Mendelian i nterpretation of variation at the Pgi-2 locus and the two Pgm loci-obs erved segregation patterns did not deviate from Mendelian expectations . At Tpi-1, however, significant deviations from expected Mendelian ra tios were observed in half of the crosses. One of the deviations occur red in a heterozygote by homozygote cross, while three (plus one borde rline) deviations occurred in heterozygote by heterozygote crosses. Si gnificant heterogeneity was also detected in the latter crosses, becau se the segregation ratios were skewed towards different homozygote cla sses. The results suggest that some form of postzygotic selection may be operating at Tpi-1. While further experimentation is required befor e we can explain these deviations, we present evidence which suggests that the biases and their directions are associated with the female, a nd not the male lines used in the crosses.