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.

The proportion of unpigmented coat on the trunk was determined from photographs of 38 German Simmental and 627 German Holstein bulls distributed over three generations. All 665 animals were members of 18 Holstein and 3 Simmental half-sib families. A Bayesian estimation of heritability yielded a posterior mean of 0.88 and a standard error of 0.08. A quantitative trait loci (QTL) scan over all chromosomes covered by 229 microsatellite marker loci (2926 cM) was performed by fitting a multiple marker regression model to 625 observations from the youngest generation in 18 families. On chromosome 6 a QTL for the proportion of white coat with large effects (experiment-wise error probability < .0001) was found and a less important one on chromosome 3 (chromosome-wise error probability < .009). Chromosome 6 is known to harbor the KIT locus (receptor tyrosinase kinase), which is associated with various depigmentation phenotypes in mice, humans, and pigs. Similarity of phenotypic KIT effects in other species and synteny with the reported QTL suggest that KIT is a serious candidate gene for the degree of spotting in cattle. The results are also discussed with respect to resistance to solar radiation, heat stress, and photosensitization.

A total of 419 individuals of four breeds with differing fecundity (Rhoenschaf, Merinolandschaf, East Friesian Milksheep, Romanov) and several wild sheep of the Ovis musimon, 0. orientalis, 0. vignei and 0. ammon groups were screened for genetic variation at the PA-inhibin (INHBA) locus with up to 11 enzymes. The four breeds differed significantly (P < 0.001) in TaqZ allele frequencies. The frequency of the TaqZ A allele coincided with the average litter size in each breed.

MONTFORT et al. 1992). Nucleotide sequence polymorphism at the a-PAor bB-inhibin loci could lead to differences in the expression of these genes, or structurally different gene products, with subsequent influences on ovulation rate in sheep breeds with differing fecundity. The latter notion is supported by results presented by FLEMING et al. (1992) who detected significantly higher P,-inhibin mRNA levels in follicles of FecB gene carriers compared to controls. Although the INHBA locus was excluded as the site of the FecB mutation (MONTGOMERY et al. 1993), different inhibin alleles could nevertheless contribute to differences in ovulation rate in other sheep breeds. The objective of this study was the identification and characterization of a-, PAand &inhibin alleles as QTL candidates for litter size in sheep. Materials and methods An i m a 1 sA total of 898 sheep of 5 breeds (Merinolandschaf, East Friesian Milksheep, Rhoenschaf, Romanov, Heidschnucke) with different reproductive performance were used in this study. Animals of the Merinolandschaf-and Rhoenschaf breed were maintained at the research station 'Oberer Hardthof', samples from other breeds were obtained on private farms. Two to 10 lambing records per sampled ewe were used to calculate the mean litter size of each breed. Several wild sheep (0. musimon, 0. ammon, 0. vignei) were included as controls. In addition, 123 individuals of the 'AgResearch International Mapping Flock' were used for linkage mapping of the inhibin genes. U.S.

A total of 419 individuals of four breeds with differing fecundity (Rhoenschaf, Merinolandschaf, East Friesian Milksheep, Romanov) and several wild sheep of the Ovis musimon, 0. orientalis, 0. vignei and 0. ammon groups were screened for genetic variation at the PA-inhibin (INHBA) locus with up to 11 enzymes. The four breeds differed significantly (P < 0.001) in TaqZ allele frequencies. The frequency of the TaqZ A allele coincided with the average litter size in each breed.