ESTIMATING WITHIN-LOCUS NONADDITIVE COEFFICIENT AND DISCRIMINATING DOMINANCE VERSUS OVERDOMINANCE AS THE GENETIC CAUSE OF HETEROSIS

Testing (over) dominance as the genetic cause of heterosis and estimat ing the (over)dominance coefficient (h) are related. Using simulations , we investigate the statistical properties of MUKAI'S approach, which is intended to estimate the average ((h) over bar) of h, across loci by regression of outcrossed progeny on the sum of the two correspondin g homozygous parents. A new approach for estimating (h) over bar is al so developed, utilizing data on families formed by multiple selfed gen otypes from each outcrossed parent, thus not requiring constructing ho mozygotes. Assuming constant mutation effects, h can be estimated accu rately by both approaches under dominance. When rare alleles have low frequencies at any polymorphic locus, MUKAI'S approach can estimate h accurately under over(under)dominance. Therefore, the (over)dominance hypothesis for heterosis can be tested by estimating h, under either d ominance or overdominance at all genomic loci. However, this is invali d dth more plausible mixed dominance and overdominance at different lo ci. Estimating the variance of h, across loci is also investigated. In self-compatible outcrossing populations with mutations of variable ef fects and lethals, our new approach is better than MUKAI'S, not only b ecause of not requiring homozygotes but also because of the better sta tistical performance reflected by the smaller mean square errors of th e estimates.