Research Update - Animals and Animal Health

The National Animal Genome Research Program (NAGRP), recently approved as a USDA regional research project, has as a general goal the determination of the genetic makeup of various economically important domestic animals. Specific objectives of the program are (1) to improve our understanding of the structure and organization of specific genes, (2) to identify and characterize genes controlling important metabolic processes (such as growth, aspects of reproduction, and milk production), and (3) to assign these genes to specific locations on chromosomes, so that they can be more easily manipulated in breeding programs designed to enhance expression of specific traits.

Integral to the process of genome mapping is the detection and characterization of "markers." Markers are sequences of DNA with unusual patterns or characteristics that are easily recognized, and the position of specific genes can be determined by ascertaining the location of the gene relative to a marker. Some have variable number tandem repeats; microsatellite markers are repeats of a simple DNA sequence (such as CACACACA, where C and A are the bases cytosine and adenine, respectively). Other markers may be identified on the basis of conformational differences.

Responsibility for the various domestic species has been spread out over the geographic regions of the U.S., each supervised by an administrative advisor. The Animal Genome Technical Committee involves 51 scientists at 27 locations, and the industries for which these studies are relevant have been actively supportive of the program.

Committees representing the major animal groups (swine, sheep, cattle, and poultry) are developing computer databases similar to that available for mice. These will serve as banks for genomic data representing the entire array of genes of a particular animal. The data will provide a basis for comparative studies among animals, to facilitate correlations between genes and their functions, and also to determine the relative positions of genes in the DNA sequence.

The committee responsible for swine genome research has made significant progress in development of a genetic linkage map, with 400 markers already identified. The immediate goals for this committee include continuing to develop a genetic linkage map and to produce swine cells that can grow independently in a laboratory setting to allow for constant availability. The swine database, USPIGBASE, is already available for use.

Several genetic linkage maps for cattle have been produced, and these cover approximately 90% of the bovine genome. The U.S.-developed map contains 313 markers, and several hundred cattle microsatellite markers have been identified in the past year. The "international" map has 201 areas of genetic diversity and is the result of an international collaboration involving ten laboratories in seven countries. A major goal for the immediate future is to develop a consensus linkage map, combining information from all independent maps now available, and to subsequently develop a database from this information.

The committee directing the mapping of the poultry genome is striving to develop a consensus genetic linkage map of chickens, with many easily identified markers, and to extend this map to other poultry of economic importance. Further, this map will be used to identify genes responsible for specific traits, to work with industries to develop effective applications for this knowledge, and to enhance progress in all of these areas through the sharing of information via a database. Recent efforts have seen the number of known markers increase to 230, and efforts to produce a consensus linkage map have begun, using several maps now available.

Researchers in the sheep genome project have been successful in developing genetic linkage maps containing several hundred markers, and work on a consensus genetic linkage map is underway.

Animal genetics and gene mapping have received major support through the National Research Initiative Competitive Grants Program (NRICGP) of the USDA. One primary objective of the NRICGP is to increase our understanding of the structure, organization, function, expression, and regulation of genes. Further knowledge in these areas will help to maintain genetic diversity, improve animal productivity and efficiency, locate economically important production traits (including size, reproductive vigor, and genetic diseases), and finally to provide methods for utilizing this information to select for desired characteristics in animals.

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