Cross-breeding animals by nature's waymay seem slow and quaint to genetic engineers who do it in a Petridish while you wait.Animal scientists from four European universities have crossed twowild boars with eight "Large White" domesticated sows. These matingsproduced four male and 22 female second-generation offspring. Thenthe researchers performed genome analysis on the 200 third-generationprogeny. Using sophisticated statistical probes, they determined thatthe gene loci governing growth and fat deposition reside on porcinechromosome 4.Their report in today's Science concludes: "The large effect of thechromosome 4 QTL (quantitative trait loci) makes it a potential modelfor human obesity." This human condition, they noted, "is an importantpolygenic syndrome with a strong environmental influence."Quantitative genetic variation, they added, is the major factor in manypopulational differences of medical and agricultural significance."This study," the paper stated, "illustrates the power of genome analysisin finding the chromosomal location of genes with phenotypic effects."In a porcine parallel with humans' current drive to reduce weight forsex appeal and health, pig farmers in Western countries are practicing"an intensive artificial selection for high growth and leanness," theScience paper noted.The report says modern domestic swine tend to put on less fat thantheir wild ancestors. Using detailed linkage maps based on more than100 DNA markers along 15 of the pigs' 18 autosomes (non-sexchromosomes), with respect to birth weight, growth rate, fat depositionand length of small intestine, the researchers found "large effects" onthese factors in chromosome 4 (for which the human counterpart ischromosome 1).The length of small intestine in swine correlates directly with growthand has increased with domestication. In the eight Large White sows, itaveraged 21.2 meters; in their 200 grandchildren, 17.5 meters, whichreflects the wild boar's heavyweight genetic influence.In the analysis, the investigators explained, they used the geneticmarker data to calculate the chances of each third-generation piginheriting none, one or two gene variants (alleles) from each parentalbreed for an unobserved QTL at a given position in the genome.It remains to be determined whether the apparent concentration of theseeffects on chromosome 4 "may constitute a single gene with a largeeffect or a cluster of linked genes, each with a smaller effect."Franklin Loew, dean of Tuft University's school of veterinarymedicine, told BioWorld that he finds the pig findings in Science "avery innovative and creative approach." Loew is also president of thefor-profit Tufts Biotechnology Corp., which is developing a researchpark at its Grafton campus 30 miles west of Boston.The dozen authors collaborating in the international project are fromSweden's University of Agricultural Sciences in Uppsala; theUniversity of Edinburgh, Scotland; INRA (National Institute ofAgronomic Research) in Jouy-en-Josas, France; and Denmark's RoyalVeterinary and Agricultural University in Copenhagen.
-- David N. Leff Science Editor
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