Understanding the genetic architecture of a quantitative trait in gymnosperms by genotyping haploid megagametophytes

The gymnosperms are a group of plants characterized by a haploid female gam etophyte (megagametophyte). With the function of bearing the female ga mete s and nourishing the developing embryo, the megagametophyte has provided a simple way to understand the genetics of gymnosperm species using biochemic al or genetic markers. In this paper, a quantitative genetic approach is pr oposed to study the genetic architecture of a quantitative trait in gymnosp erms by taking advantage of the megagametophyte and the concept of average effect of a gene. Average effect describes the value associated with an all ele carried by an individual and transmitted to its offspring. Through the genetic dissection of the average effect and genetic variance associated wi th a gamete carrying candidate genes, this approach can provide estimates o f basic population genetic parameters, such as additive, dominant and epist atic effects, allelic frequencies and linkage disequilibrium. The candidate genes, known through their major mutant phenotype, have been reported in g ymnosperms. An example for a candidate gene affecting lignin biosynthesis w as applied to demonstrate the statistical procedures of the approach and it s advantage. The conditions upon which the approach can be effectively used are discussed.