Eisen, a William Neal Reynolds Professor, says his research team s success in locating genes affecting mouse reproduction and growth will lead them to locating similar information in the genomes of other mammals. The term genome refers to an organism s total genetic code. Genomics is the study of the total set of genes of each organism, as well as those genes functions. The ability to locate specific genes, and to determine the relationship between genes and performance parameters, could lead to tremendous productivity strides in livestock species such as swine and cattle, Eisen says. To find the appropriate genes, researchers scan the genome to locate quantitative trait loci, or QTL, which are regions in chromosomes that contain specific genes that influence quantitative traits, such as average daily weight gain in cattle or pigs, litter size in swine or milk production in cattle.
Quantitative traits are characteristics controlled by many genes.
Each QTL might have only a small effect on a trait, but that effect could be important. The situation is further complicated because the expression of complex traits whether in livestock, mice or humans is dictated by many genes interacting with each other and with the individual s environment, Eisen notes. Researchers first identify the QTL s exact location, then identify the genes functions that relate to gene expressions such as growth rate, he says. And in a process called marker-assisted selection, researchers also use easily measured marker loci near the QTL to help select an economically important trait more accurately. Eisen s work with his postdoctorate associate, Frank Siewerdt, and with Dr. Daniel Pomp of the University of Nebraska has identified QTL for growth and reproduction in female mice.