Bias and power in the estimation of a maternal family variance component in the presence of incomplete and incorrect pedigree information

Several studies over the last 15 yr have estimated the magnitude of cytopla smic inheritance of production and type traits in dairy cattle. Pedigree in formation can be used to assign maternal lineages, and the between-maternal lineage variance is then assumed to be an estimate of cytoplasmic inherita nce. Two potential sources of bias and reduction of the power of estimation of cytoplasmic inheritance using such a method are 1) incomplete and 2) in correct pedigree information being used in the assignment of maternal linea ges. The theoretical bias introduced by these two sources of error is inves tigated and the results of a simulation study varying the number of familie s, the percentage of pedigree errors, and the level of incomplete lineage a ssignment are presented. Pedigree errors were found to have the biggest imp act. A pedigree error rate of 8% per generation would result in a 75% reduc tion in the estimable magnitude of a 5% true component of variance after ni ne generations. The effect that these mechanisms have on the power of estim ation are discussed and investigated by simulation. It was concluded that u sing historical pedigree, with incomplete and incorrect maternal family inf ormation, to assign maternal lineage would cause a downward bias in the mag nitude of the cytoplasmic effect estimated. In the future, it will be possi ble to overcome pedigree problems by using molecular information to directl y assign cytoplasmic lineage groups.