CONSIDERATIONS ON GENETIC CONNECTEDNESS BETWEEN MANAGEMENT UNITS UNDER AN ANIMAL-MODEL

Connectedness among management units (e.g., herds or regions) is of co ncern in genetic evaluation. When genetic evaluation is under an anima l model, connections occur through A, the numerator relationship matri x. It is argued that the most appropriate measure of connectedness is the average prediction error variance (PEV) of differences in EBV betw een animals in different management units. It is shown that PEV of dif ferences is influenced by average genetic relationship between and wit hin management units, which in turn affects the variances of estimates of differences between management unit effects. When PEV of differenc es cannot be computed, use of one of three alternative measures is pro posed; the gene-flow method that measures the exchange of genes betwee n management units, measurement of genetic drift variance based on ave rage relationships between and within management units, and measuremen t of the variance of estimated differences between management units ef fects. These were correlated with PEV of differences in a test simulat ion. The gene-flow method, which is simplest to compute, had the lowes t correlation (.671). The drift variance and variance of management un it effects methods were highly correlated with PEV of differences (.92 4 and .995, respectively).