Among the known genes, 638 (83 percent) could be identified as identical to human genes that also have positional information on human chromosomes, the researchers reported. Knowing the order of the same genes on the chromosomes of humans and cattle permitted the construction of the first "whole-genome comparative map" and revealed large regions of conservation of gene order in the two genomes. An examination of the comparative map revealed up to 149 conserved chromosome segments in humans and cattle, including four whole chromosomes that appear to have the same genes in both species, despite the two species being separated by more than 60 million years of evolution.
Among other firsts in the report were the identification of up to 48 novel genes, predicted mapping of 48 unmapped human genes on the basis of the cattle-map position, and the number of chromosome rearrangements during evolution resulting in the present organization of the cattle and human genomes.
Eventually, Lewin said, the cattle genome will be completely sequenced, ultimately leading to a more detailed picture of the evolutionary events that distinguish the different mammals. "In the end" he said, "we will understand the molecular genetic basis for the major phenotypic differences among the mammals. This will have enormous scientific and practical significance, particularly in the area of food safety, animal health, and the competitiveness of our domestic beef and dairy industries."