THE OCCURRENCE AND SIGNIFICANCE OF EPISTATIC VARIANCE FOR QUANTITATIVE CHARACTERS AND ITS MEASUREMENT IN HAPLOIDS

Epistatic genetic variance for quantitative trails may play an importa nt role in evolution, but detecting epistasis in diploid organisms is difficult and requires complex breeding programs and very large sample sizes. We develop a model for detecting epistasis in organisms with a free-living haploid stage in their life cycles. We show that epistasi s is indicated by greater variance among families of haploid progeny d erived from individual diploids than among clonally replicated haploid sibs from the same sporophyte. Simulations show that the power to det ect epistasis is linearly related to the number of sporophytes and the number of haploids per sporophyte in the dataset. We illustrate the m odel with data from growth variation among gametophytes of the moss, C eratodon purpureus. The experiment failed to detect epistatic variance for biomass production, although there was evidence of additive varia nce.