Abstract

his paper describes a recently initiated European project for the production of a gene map of the pig, with polymorphic molecular genetic markers evenly spaced through the genome and landmark loci physically assigned to chromosomes. Potential benefits include: - Understanding the organisation and action of genes controlling valuable quantitative traits. - The ability to improve breeding stock using marker assisted selection. - The possibility of isolating for study or manipulation important genes by 'reverse genetics'. - Studying the genomic organisation and evolutionary relationships of pigs, man and other mammals. - The development of porcine models of human disease. The pig has several advantages over other farm animal species for genetic mapping including a well defined karyotype, large full-sib families, short generation interval, the availability of diverse genetic stocks and an advanced breeding industry capable of exploiting developments. European commercial breeds, Chinese Meishan pigs and the European Wild Boar will be used to create reference families. The genetic distance between these stocks will facilitate the isolation of informative genetic markers and allow genes controlling the physical differences in economically important traits to be studied. The comparative conservation of DNA sequences and linkage relationships between mammalian species allows the porcine genetic map to be built on a skeleton of molecular markers which have already been mapped in man or in the mouse. This can be fleshed out with molecular markers based on minisatellite or microsatellite loci (variable number tandem repeat loci or VNTRs) which are very polymorphic and thus highly informative for linkage studies both between and within breeds. The polymerase chain reaction (PCR) for typing microsatellite loci provides the prospect of rapid, automated genotyping of animals for marker lod in the future. A sample of cloned marker sequences will be physically assigned to chromosomes using hybrid cell lines and regionally located by in situ hybridization to provide at least one proximal and distal landmark locus on each chromosome arm. The porcine karyotype is well suited to chromosome sorting using fluorescence activated cell sorting (FACS) and a porcine flow karotype will be developed allowing rapid assignment of cloned sequences to chromosomes and the production of chromosome specific libraries. In the final stage of the production of the molecular map, genes controlling physical variation (quantitative trait loci or QTLs) will be mapped and studied. Located genes or chromosomal segments of major economic value can be selected between or within breeds using marker assisted selection. Work on the production of the gene map has begun. Heterologous and homologous probes are being used to examine the genetic distance between the breeds involved and are being located by in situ hybridization. The production of reference families is under way. Porcine locus specific VNTR probes are being isolated. Hybrid somatic cell lines are available and a porcine flow karyotype is being developed. It is envisaged that a low resolution genetic and physical map could be achieved in 3-4 years, with preliminary mapping of QTLs of large effect possible shortly afterwards.

Chris S Haley, Alan L Archibald, Leif Andersson, A. A Bosma, W. Davies, M. Fredholm, H. Geldermann, M. Groenen, I. Gustavsson, L. Ollivier, E. M Tucker, A. van de Weghe

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XIII. Plenary lectures, molecular genetics and mapping, selection, prediction and estimation., , 67–70, 1990
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