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.

A cattle genetic linkage map was constructed which covers more than 95 percent of the bovine genome at medium density. Seven hundred and forty six DNA polymorphisms were genotyped in cattle families which comprise 347 individuals in full sibling pedigrees. Seven hundred and three of the loci are linked to at least one other locus. All linkage groups are assigned to chromosomes, and all are orientated with regards to the centromere. There is little overall difference in the lengths of the bull and cow linkage maps although there are individual differences between maps of chromosomes. One hundred and sixty polymorphisms are in or near genes, and the resultant genome-wide comparative analyses indicate that while there is greater conservation of synteny between cattle and humans compared with mice, the conservation of gene order between cattle and humans is much less than would be expected from the conservation of synteny. This map provides a basis for high-resolution mapping of the bovine genome with physical resources such as Yeast and Bacterial Artificial Chromosomes as well as providing the underpinning for the interpolation of information from the Human Genome Project.

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Summary Genetic variability within four Belgian pig breeds, (Landrace (BL), Negative (BN), Piétrain (P), and Large White (LW)) was investigated using seven microsatellite loci. Differences in allele frequencies indicate each breed's particular identity. Computation of polymorphism information contents (PIC), theoretical heterozygosities, effective numbers of alleles, and probabilities of encountering, at random, two identical individuals in each breed revealed a variability, decreasing in the order LW, BN, BL, and P. Five types of genetic distance between the breeds were also calculated. Two‐by‐two breed comparisons indicated some distances to be rather important, confirming the breeds' morphological differences. BL and BN show the closest resemblance, while P is the most distant breed. The chances of encountering, at random, two identical individuals among two breeds are small, and confirm the conclusions resulting from the genetic distances. The efficiency of the microsatellites in parentage control is high. Zusammenfassung 7 Microsatellitsystemen studiert in 4 Belgische Schweinerassen Anhand von 7 Microsatellitsystemen wurde die genetische Variabilität innerhalb 4 Belgischer Schweinerassen (Landrasse [BL], Negativ [BN], Pietrain [P] und Large White [LW] untersucht. Unterschiede in Allelhäufigkeiten deuten auf die besondere Identität jeder einzelnen Rasse. Berechnung von Polymorphismus, Informationsinhalt (PIC), theoretischer Heterozygotiewerte, wirksamer Anzahl von Allelen und Wahrscheinlichkeit zweier identischer Individuen in jeder Rasse brachte Hinweise auf abnehmende Variabilität in der Reihenfolge von LW, BN, BL und P. Ausserdem wurden 5 Arten genetischer Distanzen zwischen den vier Schweinerassen berechnet. Bei paarweisem Vergleich zeigten diese Distanzen sich als ziemlich gross, so dass damit die morphologischen Differenzen zwischen den Rassen bestätigt werden. BL und BN haben die engste Verwandtschaft und P ist am weitesten entfernt von BL, BN und LW. Die Wahrscheinlichkeit, zufällig zwei identische Tiere in zwei Rassen zu finden, fehlt praktisch und bestätigt die Schlussfolgerungen, die sich aus den genetischen Distanzen ergeben. Die Microsatelliten sind sehr zweckmässig anwendbar in der Abstammungskontrolle.

A detailed physical map of the porcine MHC class III region on Chr 7 was constructed with a panel of probes in a series of hybridizations on genomic pulsed field gel electrophoresis (PFGE) Southern blots. A precise organization of the 700-kb segment of DNA between G18 and BAT1 can now be proposed, with more than 30 genes mapped to it. Comparison of this region with homologous regions in human and mouse showed only minor differences. The biggest difference was observed in the CYP21/C4 locus with only one CYP21 gene and one C4 gene found, whereas in human and mouse these genes are duplicated. These results show the class III region is very well conserved between pig, human, and mouse, in contrast with the class I and class II regions, which seem more prone to rearrangements.