Four lambda clones (lambda G11, lambda C4, lambda G14 and lambda G17) from the porcine MHC class III region were labelled with either biotin-14-dATP or digoxigenin-11-dUTP and hybridized in two different combinations to DNA fibres. The latter were prepared from agarose-embedded porcine peripheral lymphocytes lysed with proteinase K, then spread and fixed on poly-L-lysine-coated slides. Hybridization signals thus obtained confirm the order of the clones previously reported using pulsed-field gel electrophoresis (PFGE). Measurements of probe sizes, gap distances between probes and total length of DNA encompassing the probes were made. Three different methods, namely relative length, Watson-Crick standard and probe size standard-based conversions, were used to estimate the parameters in kilobases. These methods of data conversion were compared with each other and with the available PFGE data, and their utility and accuracy were evaluated.

The polymorphism of 23 microsatellites in the four main cattle breeds in Belgium (Holstein Friesian, Belgian Blue, Belgian Red Pied and East Flemish) was analysed. Heterozygosity, polymorphism information content, the effective number of alleles, exclusion probability and the probability of genotypic identity for two random individuals were calculated for all microsatellites and all breeds. The Belgian Blue breed is generally a little less polymorphic in comparison with the other three breeds. Estimates of the genetic distances between these breeds confirmed the widely accepted proposition that the Belgian Blue is the most genetically distinct of these breeds. The three other breeds are likely to become one population, given current breeding strategies. Exclusion probabilities in parentage control cases are > 0.9999 in all four breeds when all 23 microsatellites are used and > 0.98 with only the two most polymorphic multiplexes.

A set of 33 cattle microsatellite primer pairs was tested with the DNA of American bison from a captive population in Belgium and evaluated for usefulness in parentage testing. Two primer sets did not amplify and three were monomorphic. Among the polymorphic markers, the number of alleles ranged from two to nine. Heterozygosity, polymorphism information content (PIC) and probability of exclusion (PE) values were low by comparison with those obtained with the same markers in cattle. Two methods of estimating PE were used, one which assumed equal allele frequencies between parental sexes and another which took into account differences in allele frequencies between parental sexes. An internationally accepted set of nine microsatellites gives cumulative PE values of 0.98 and 0.97, respectively, for the two methods. The potential of this marker set to identify bison x cattle hybrids is discussed. Because bison and cattle have a common ancestor, these microsatellites are a useful way to establish genetic distances and can lead to the construction of phylogenetic trees.

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.

Introduction Genetic variation is being used extensively for individual identification and linkage analysis, and may be useful for interpopulation studies. Previously, blood groups and biochemical variants in blood cell and serum proteins have been used to study (evolutionary) relationships in mammals. But genetic divergence and gene flow among closely related populations are difficult to measure with these classical markers because their mutation rate is so low that new mutations have not had sufficient time to appear and become fixed. So they have a small number of alleles and a relatively low level of heterozygosity. These markers are now replaced by DNA markers, mostly microsatellites. These microsatellite loci are useful genetic markers at which alleles differ in length due to differences in the number of short sequence motifs arranged adjacent to one another. They are abundantly distributed throughout the mammalian genome. They have a large number of alleles, a high level of heterozygosity and are inherited in true Mendelian fashion. These characteristics make them valuable for parentage control, linkage analysis, genome mapping and phylogenetic studies. In terrestrial vertebrates with limited mobility, genetic differentiation often increases with the distance between populations or corresponds to the extent of geographic and habitat barriers (R oy et al. 1994). Investigations of short tandem repeats yield a considerable volume of genetic data regarding the similarities and divergence times of different cattle populations. Microsatellite markers are suitable for the estimation of these parameters as they are not generally subject to direct selection and environmental influences. Computation of genetic distances based on data from several loci can be used to evaluate the taxonomic relationship between populations. The aim of this study was to estimate the relative genetic variability between Belgian cattle breeds and to reconstruct the evolutionary relationship among them, also using two small genetically isolated cattle‐like populations.