In the eigenvector v l = (vl ,1,vl ,2,…,vl ,M)′, its mth element vl,m, called loading, 1≤m≤M, reflects the influence of mth marker on shaping v l. Following suggestions from the WTCCC, the loading of every SNP on the v l can be used to search for chromosomal regions where variation pattern among samples would determine the lth PC direction. A PC that reflects regional genetic variation will be evidenced by a spike of high loadings for markers in that chromosomal region.
