**3.2 The RH mapping**

Radiation hybrid (RH) mapping is a kind of somatic cell genetics tool for mapping candidate genes into a framework of microsatellites/sequence-tagged sites. First, RH panels are constructed by using a lethal dose of X-rays to fragment the chromosomes of the donor cell and the chromosome fragments with known genetic markers are retained randomly in the host cells. The frequency of breakage between pairs of markers in a panel of RH clones can be used to calculate the relative physical distances of the genetic markers or genes. Several porcine RH panels have been produced, among which the whole-genome highresolution IMpRH panel constructed by Yerle et al. (1998) is the most frequently used one.

The porcine *TRHR* gene was localized to the microsatellite *SW969* on chromosome 4 by RH mapping using the IMpRH panel (Jiang et al., 2011). 44 Quantitative trait loci affecting BFT, daily gain, and carcass and meat quality traits have been mapped to the same region. *TSHR* gene has been mapped between microsatellites *SW1083* and *SW581* on porcine chromosome 7 (Sato et al., 2006), and 50 QTLs including BFT, ADG, carcass length and muscle related traits have been mapped to the same position.
