An Experimental Evaluation of Genetic Correlation

Abstract

Heritability and genetic correlations realized from both single-trait and antagonistic index selection were compared with paternal half-sib estimates. Primary attention was focused on the genetic correlation between six-week body weight and six-week tail length. Parameters realized from single-trait selection were in excellent agreement with paternal half-sib estimates. However, the realized genetic correlation between six-week body weight and six-week tail length obtained from index selection was significantly greater than the other estimates. Differential inbreeding levels and realized selection intensities were considered and rejected as being causative factors for these results. Linkage disequilibrium probably was not a factor either, as the base population had been randomly mated and randomly selected with a large effective population size for many generations. It was concluded that with antagonistic index selection, the pleiotropic effects of genes may be more powerful in retarding response in aggregate genotype than current theory would suggest. Replication of all selected and control lines allowed the use of between-line estimators of sampling variances of realized genetic parameters in the above comparisons. Generally, standard errors of realized genetic parameters were much smaller than corresponding paternal half-sib standard errors. Thus, selection was an efficient method of estimation.

Population Size and Selection Intensity Effects on Long-Term Selection Response in Mice

“…The realized genetic correlation between number born and postweaning gain of 0.35 was less than the paternal half-sib estimate of 0.58 . The realized correlation of 1.02 between postweaning gain and six-week body weight was similar to the estimate of 0.93 pooled from studies of HANRAHAN and EISEN (1973) andRUTLEDGE. EISEN and.…”

Selective breeding as a tool to probe skeletal response to high voluntary locomotor activity in mice

“…Evolution in the laboratory (or garden) by way of selection experiments is an increasingly accessible methodology used to study traits of interest, both morphologic and physiologic (Garland and Carter 1994;Bennett and Lenski 1999;Gibbs 1999;Feder et al 2000;Bennett 2003;Garland 2003; Rose manuscript in review). Well-documented selection experiments (Hill and Caballero 1992) on morphological traits in vertebrates began 460 years ago with the work of MacArthur, Rutledge, Eisen, Atchley, and their collaborators (MacArthur 1944a(MacArthur , 1944bRutledge et al 1973Rutledge et al , 1974Eisen and Bandy 1977;Atchley et al 1982Atchley et al , 1984Eisen 1986Eisen , 1987aEisen , 1987b. Most early studies involved selection for body mass or growth rate, and several of these examined the correlated response of skeletal morphology.…”

“…Most early studies involved selection for body mass or growth rate, and several of these examined the correlated response of skeletal morphology. For example, significant changes in tail length (MacArthur 1944a(MacArthur , 1944bRutledge et al 1973Rutledge et al , 1974 and foot length (MacArthur 1944a(MacArthur , 1944b were found during selection on body size in mice.…”

How much do genetic covariances alter the rate of adaptation?

“…r 12 ZK0.5) will still allow for some adaptation-a fact noted by several investigators who have applied artificial selection to genetically correlated traits and still obtained a response to selection. These results come from agricultural systems (poultry : Nordskog 1977), model systems (mice: Cockrem 1959;Rutledge et al 1973) and evolutionary and ecological systems (flour and dung beetles, butterflies, and short-lived plants: Bell & Burris 1973;Stanton & Young 1994;Emlen 1996;Beldade et al 2002;Conner 2003;Frankino et al 2005). As such, the relevant comparison is not whether any adaptation can occur, but how much occurs relative to a scenario with a different covariance structure.…”