9707372 McCauley This project will investigate the genetic determinants of sex expression in natural populations of Silene vulgaris, a gynodioecious plant. In plants gynodioecy, or the presence of female and hermaphroditic individuals in the same population, is fairly common. Sex determination in gynodioecious plants is often a consequence of the interaction of genes in the cytoplasm that eliminate male function, and genes in the nucleus that restore it. The study of S. vulgaris will consist of two parts. First, a complex series of "tester" crosses will be conducted in order to characterize genetic diversity at the cytoplasmic and nuclear gene loci. Second, cytoplasmic molecular markers will be developed so that numerous individuals can be classified according to the male sterility types identified by the crosses. This will enable a rapid characterization of the genetic composition of populations. One observation that is often made of gynodioecious species is that the relative numbers of females and hermaphrodites (the sex ratio) can vary dramatically from place to place. One goal of the crosses and molecular studies is to understand the genetic basis for population to population variation in the sex ratio. This will be one of just a few investigations of the genetics of gynodioecy in natural plant populations. The use of male sterility factors to manipulate the gender of economically important crop plants is an important tool in plant breeding, yet the phenomenon is not well understood in nature. In addition to potential benefits to plant breeders, this study will also be of value to the field of basic population genetics, in that it will contribute to an understanding of how genetic diversity is maintained within species.
