Cell proliferation in the SGZ of BXD RI strains and QTL analyses. (A) The number of BrdU+ cells in the SGZ (± SEM) of 61 BXD RI strains (white bars) and their parental strains, C57BL/6 J (red bar), and DBA/2 J (green bar). The sample size per strain is indicated in the bars. Whole-genome scan LRS plot generated from QTL mapping of the unadjusted SGZ cell proliferation data (B) and the adjusted data corrected for age effects (C). The x-axis represents the chromosomes 1–19, & X (top panel) and their physical maps in megabases (bottom panel). The y-axis and the blue line depict the LRS, which indicates the strength of association between genotypes of markers across the genome and the phenotype. The light red and gray horizontal lines mark the significant (P = 0.05) and suggestive (P = 0.63) threshold, respectively. Whole-genome interval mapping of unadjusted SGZ proliferation data (B) and the SGZ proliferation data adjusted for age (C) identified no significant QTL but revealed suggestive QTLs on Chr 1 (40-59 Mb), Chr 5 (104.5-119.5 Mb), and Chr 9 (71–83.7 Mb).