Linkage maps of porcine chromosomes 3, 6, and 9 based on 31 polymorphic markers

Genetic variation in the porcine myogenin gene locus

The myogenin (MYOG) gene fulfills a key function in muscle differentiation by controlling the onset of myoblast fusion and the establishment of myofibers. In meat-producing animals like pigs and cattle, myofiber numbers have been related to growth capacity. We have characterized the porcine MYOG gene to detect genetic variation at this locus and to relate it to growth characteristics. MYOG gene fragments were isolated by PCR on genomic DNA and by screening a genomic library with a mixture of the four human MyoD cDNA fragments. Both the exons and promoter region were very similar to the human and mouse genes. Southern blot analysis of 105 unrelated pigs revealed three polymorphic MspI sites, located in the promoter region, the second intron, and at the 3' side of the gene. PCR-RFLP tests detecting four MYOG alleles were developed. PCR analysis of a panel of pig-rodent somatic cell hybrids confirmed the genetic localization of MYOG on pig Chromosome (Chr) 9. The PCR-RFLP tests and microsatellite markers on Chr 9 offer the possibility to genotype large numbers of pigs for studies of genetic linkage to meat deposition and growth characteristics.

Partial characterization of porcine obesity gene (OBS) and its localization to chromosome 18 by somatic cell hybrids

Degenerate primers based on human and mouse obesity gene (OBS) sequencing data were used in the reverse transcriptase-polymerase chain reaction (RT-PCR) of total RNA from pig white adipose tissue. Both strands of the resultant pig- specific 325 bp DNA fragment were sequenced. Comparison of the obtained sequence with known sequences revealed an 86% identity with the human and 84% identity with the mouse OBS cDNA. The OBS gene was physically mapped to pig chromosome 18 by PCR analysis of somatic cell hybrids, using pig-specific primers. This result is consistent with the recent assignment of the human OBS gene to chromosome 7 and the observation made by comparative mapping that by using a human chromosome 7 specific library two segments of conserved synteny were detected on porcine chromosomes 9 and 18. We conclude the border of conserved synteny to be in the 7q31-7q32 region of the human chromosome.

A comprehensive linkage map of the pig based on a wild pig-Large White intercross

A comprehensive linkage map, including 236 linked markers with a total sex-average map length of about 2300 cM, covering nearly all parts of the pig genome has been established. Linkage groups were assigned to approximately all 18 autosomes, the X chromosome and the X/Y pseudoautosomal region. Several new gene assignments were made including the assignment of linkage group U1 (EAK-HPX) to chromosome 9. The linkage map includes 77 types I loci informative for comparative mapping and 72 in situ mapped markers physically anchoring the linkage groups on chromosomes. A highly significant heterogeneity in recombination rates between sexes was observed with a general tendency towards an excess of female recombination. The average ratio of female to male recombination was estimated at 1.4:1 but this parameter varied between chromosomes as well as between regions within chromosomes. An intriguing finding was that blood group loci were overrepresented at the distal ends of linkage groups.

Chromosomal assignment of porcine EAD, EAO, LPR and P3 genes by linkage analysis

A two-point linkage analysis was performed between blood group (14), allotype (8), polymorphic protein (11), DNA type I (2), and microsatellite (2) loci in Wild Boar x Pietrain and Meishan x Pietrain three-generation families. The following new pairwise linkages were detected: LPR-EAN (Zmax = 60.68, theta = 0.055), EAD-GH1 (Zmax = 17.43, theta = 0.246), EAO-P3 (Zmax = 15.81, theta = 0.239), and P3-S0003 (Zmax = 5.43, theta = 0.312). This study and published mapping data enabled the localization of LPR (LPR allotype) to chromosome 9, EAD (erythrocyte antigen D) to chromosome 12, and EAO (erythrocyte antigen O) and P3 (P3 allotype) to the q arm of chromosome 6 with gene order S0003-P3-EAO, EAO being the most distal.

First international workshop on porcine chromosome 6. Report and abstracts

Recent advances in the use of microsatellite markers and the development of comparative gene mapping techniques have made the construction of high resolution genetic maps of livestock species possible. Framework and comprehensive genetic linkage maps of porcine chromosome 6 have resulted from the first international effort to integrate genetic maps from multiple laboratories. Eleven highly polymorphic genetic markers were exchanged and mapped by four independent laboratories on a total of 583 animals derived from four reference populations. The chromosome 6 framework map consists of 10 markers ordered with high local support. The average marker interval of the framework map is 15.1 cM (sex averaged). The framework map is 135, 175 and 109 cM in length (for sex averaged, female and male maps, respectively). The comprehensive map includes a total of 48 type I and type II markers with a sex averaged interval of 3.5 cM and is 166, 196 and 126 cM (for sex averaged, female and male maps, respectively). Additional markers within framework map marker intervals can thus be selected from the comprehensive map for further analysis of quantitive trait loci (QTL) located on chromosome 6. The resulting maps of swine chromosome 6 provide a valuable tool for analysing and locating QTL.

The PiGMaP consortium linkage map of the pig (Sus scrofa)

A linkage map of the porcine genome has been developed by segregation analysis of 239 genetic markers. Eighty-one of these markers correspond to known genes. Linkage groups have been assigned to all 18 autosomes plus the X Chromosome (Chr). As 69 of the markers on the linkage map have also been mapped physically (by others), there is significant integration of linkage and physical map data. Six informative markers failed to show linkage to these maps. As in other species, the genetic map of the heterogametic sex (male) was significantly shorter (approximately 16.5 Morgans) than the genetic map of the homogametic sex (female) (approximately 21.5 Morgans). The sex-averaged genetic map of the pig was estimated to be approximately 18 Morgans in length. Mapping information for 61 Type I loci (genes) enhances the contribution of the pig gene map to comparative gene mapping. Because the linkage map incorporates both highly polymorphic Type II loci, predominantly microsatellites, and Type I loci, it will be useful both for large experiments to map quantitative trait loci and for the subsequent isolation of trait genes following a comparative and candidate gene approach.

The lactase phlorizin hydrolase (LCT) gene maps to pig chromosome 15q13

A porcine 17kb genomic fragment was used as probe to map the lactase phlorizin hydrolase (LCT) gene to pig chromosome 15q13 by fluorescence in situ hybridization. Further, a three-allele TaqI RFLP was used to add the LCT gene to the proximal end of the chromosome 15 linkage map. Comparison of the human chromosome 2 gene map and the gene map of pig chromosome 15 indicates that the part of human chromosome 2 distal to the q13 band is homologous to pig chromosome 15.