New quantitative trait loci for the genetic variance in circadian period of locomotor activity between inbred strains of mice.

Provisional quantitative trait loci (QTL) for circadian locomotor period and wheel-running period have been identified in recombinant inbred (RI) mouse strains. To confirm those QTL and identify new ones, the genetic component of variance of the circadian period was partitioned among an F2 intercross of RI mouse strains (BXD19 and CXB07). First, a genomic survey using 108 SSLP markers with an average spacing of 15 cM was carried out in a population of 259 (BXD19 x CXB07)F2 animals. The genome-wide survey identified two significant QTL for period of locomotor activity measured by infrared photobeam crossings on mouse chromosomes 1 (lod score 5.66) and 14 (lod score 4.33). The QTL on distal chromosome 1 confirmed a previous report based on congenic B6.D2-Mtv7a/Ty mice. Lod scores greater than 2.0 were found on chromosomes 1, 2, 6, 12, 13, and 14. In a targeted extension study, additional genotyping was performed on these chromosomes in the full sample of 341 F2 progeny. The 6 chromosome-wide surveys identified 3 additional QTL on mouse chromosomes 6, 12, and 13. The QTL on chromosome 12 overlaps with circadian period QTL identified in several prior studies. For wheel-running period, the chromosome-wide surveys identified QTL on chromosomes 2 and 13 and one highly suggestive QTL on proximal chromosome 1. The results are compared to other published studies of QTL of circadian period.