When the use of isozyme electrophoresis became common practice, data on the genetic structure of plant populations increased rapidly. Conifers, in particular, have been well-studied because their haploid megagametophyte persists until seed maturity, which makes genetic analysis simple. Most of the early studies on the genetic structure of conifers dealt with widespread, north temperate or boreal species. One of the emerging generalities was that conifers had substantial genetic diversity within populations and only low levels of differentiation among populations. The common measure of differentiation was G ST or F ST , which yielded nearly identical values.
Genetic structure has implications for conservation.
If nearly all of the genetic variation is within populations, then reserves that protect a few, or even a single, large population will be sufficient to conserve most of the diversity. They realized that conservation of these species in Mexico would be effective only if several populations were protected. We reviewed our data on Mexican conifers, most of it unpublished, and the published results of others to determine whether population differentiation in Mexico was greater than that observed among north temperate and boreal conifers. Our studies of Mexican conifers included four pines and three spruces. For each species, isozyme electrophoresis provided genetic markers.