9520381 Mitton Effective management of plant populations (either for economic or conservation purposes) requires an understanding of the genetic differences among populations, since these differences may reflect adaptation to the local environments in which each population lives. Much of our understanding of population differentiation has been derived from the study of protein genes. This proposed research will make use of recent DNA technologies to compare the findilgs from protein genes to other types of gene, in natural populations of ponderosa pine. The data collection is straightforward, and consists of measuring the amount of genetic differentiation between populations in a north-south transect through the range of ponderosa pine from the Southwest. Genetic differences are measured by determining the frequency of DNA types ("alleles") in each population under study, from samples of needle tissue brought back to the laboratory. This study will advance our understanding in two ways. First, by comparing patterns of genetic differences between different types of genes, older findings can be tested. Theory predicts that the size of genetic differences among populations will be determined by the amount of migration and interbreeding between them. Since the amount of migration is the same for all genes, all loci should show the same magnitude of difference between populations. If not, then genes which "don't fit" are likely to be affected by some other factor, such as selection to adapt to local conditions. Second, the study will compare those genes inherited from both parents (most genes) with those inherited solely from one parent. Pines provide a unique opportunity to do this in that chloroplast DNA is inherited paternally (through the pollen), while mitochondrial DNA is maternally inherited (through the seed). By comparing the relative differences between populations for genes with these contrasting inheritance patterns, the investigators can measure the relative amount of mig ration by both seeds and pollen. It is important to understand this, because only seed migrants can found new populations, while migrant pollen is restricted to movement between existing populations.
