A high-resolution GTG-banded karyotype of the pig was obtained after methotrexate-induced cell synchronization. A diagrammatic representation of the banding pattern at the 539-band level is presented.

The porcine gene for luteinizing hormone/choriogonadotropin receptor (LHCGR) was localized to chromosome 3q2.2→q2.3 using radioactive and nonradioactive in situ hybridization. A computer-assisted image-analysis system was developed which facilitated detection of the position of silver grains and fluorescent spots on the chromosomes after in situ hybridization. Compared with autoradiographic visualization, the nonisotopic procedure proved to be more rapid, precise, and highly specific; however, nonradiographic in situ hybridization was much less efficient than the autoradiographic technique for the detection of unique DNA sequences with small probes. From these results and published gene-mapping data, it was concluded that the synteny between LHCGR and MDH1 observed in man is conserved in the pig genome.

In the pig, the linkage group around the halothane gene (HAL), composed of S-GPI-HAL-H-A1BG-PGD, has been assigned to bands p1.2→q2.2 of chromosome 6. In man, ENOl-PGD and APOE-GPI constitute two syntenic groups situated on different chromosomes (1 and 19, respectively). Since GPI and PGD are linked in the pig, we have hybridized the human cDNA probes for ENO1and APOE to pig chromosomes. These markers were assigned to pig chromosome 6, in the q2.2→q2.4 and cen→q2.1 regions, respectively, using in situ hybridization. Since GPI and APOE are situated in the same region, we combined the use of high resolution chromosome analysis and in situ hybridization to give a more precise localization in the q1.2 and q1.2→q2.1.2 regions of chromosome 6. A possible linear order of these genes is proposed.

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