A test of the complementary gene model for the control of biparental plastid inheritance in zonal pelargoniums

Zonal pelargoniums have a mixed plastid inheritance. After G × W plastid crosses, the progeny are a mixture of green, variegated and white embryos corresponding to a maternal, biparental or paternal plastid inheritance. There are two patterns of segregation: type I females produce families with a majority of green embryos, variegated intermediate and white least frequent. Type II females give rise to families in which green and white embryos are of about the same frequency and variegated the least common. The complementary gene model proposes that the alternative patterns are determined by two genes called Pr1/pr1 and Pr2/pr2 . Plants giving rise to the type II pattern contain one or two copies of the dominant alleles of both genes whereas in the absence of either one or both dominant alleles the plants are type I. The model was tested and confirmed in the classical Mendelian manner in which a single cross between two different true-breeding type I plants was followed by scoring the parents, the F 1 hybrid progeny and the F 2 and backcross generations. The results supported the interpretation that one type I parent had the genotype Pr1Pr1, pr2pr2 and the other type I parent had the genotype pr1pr1, Pr2pr2. The range, variance and confidence limits are given for the estimates of percentage maternal plastid transmission within groups of type I and type II plants in 18 segregating families.