Estimating genetic correlations in natural populations in the absence of pedigree information: Accuracy and precision of the Lynch method

Usually, genetic correlations are estimated from breeding designs in the la boratory or greenhouse. However, estimates of the genetic correlation for n atural populations are lacking, mostly because pedigrees of wild individual s are rarely known. Recently Lynch (1999) proposed a formula to estimate th e genetic correlation in the absence of data on pedigree. This method has b een shown to be particularly accurate provided a large sample size and a mi nimum (20%) proportion of relatives. Lynch (1999) proposed the use of the b ootstrap to estimate standard errors associated with genetic correlations, but did not test the reliability of such a method. We tested the bootstrap and showed the jackknife can provide valid estimates of the genetic correla tion calculated with the Lynch formula. The occurrence of undefined estimat es, combined with the high number of replicates involved in the bootstrap, means there is a high probability of obtaining a biased upward, incomplete bootstrap, even when there is a high fraction of related pairs in a sample. It is easier to obtain complete jackknife estimates for which all the pseu dovalues have been defined. We therefore recommend the use of the jackknife to estimate the genetic correlation with the Lynch formula. Provided data can be collected for more than two individuals at each location, we propose a group sampling method that produces low standard errors associated with the jackknife, even when there is a low fraction of relatives in a sample.