ONE OF THE MOST IMPACTFUL TOOLS FOR IMPROVING BEEF CATTLE GENETICS HAS BEEN AROUND FOR AS LONG AS HUMANS HAVE BEEN BREEDING PLANTS AND ANIMALS. BREEDERS HAVE LONG UNDERSTOOD THAT WHEN WE CROSS PARENTS FROM TWO DIFFERENT LINES OR BREEDS, WE OBSERVE OFFSPRING THAT CONSISTENTLY OUTPERFORM EITHER PARENTAL LINE. THIS SUPERIOR PERFORMANCE IS KNOWN AS HETEROSIS OR HYBRID VIGOR. WHILE THE RESULTS OF CROSSBREEDING ARE WELL KNOWN, THE MECHANISMS THAT DRIVE HETEROSIS ARE LESS CLEAR. WE ARE INTERESTED IN USING CATTLE TO UNDERSTAND HOW HETEROSIS WORKS AT THE MOLECULAR LEVEL. WHILE HETEROSIS IS USUALLY OBSERVED FOR MEASURED TRAITS, WE THINK IT IS ALSO LIKELY TO BE OBSERVABLE AT THE GENE EXPRESSION LEVEL. WE ANTICIPATE THAT GENES WILL HAVE INCREASED EXPRESSION IN CROSSBRED ANIMALS COMPARED TO THEIR PUREBRED COUNTERPARTS. THIS PROJECT WILL USE LAB-DEVELOPED EMBRYOS FROM A CROSS OF TWO VERY DIFFERENT CATTLE BREEDS, ANGUS AND BRAHMAN. WE WILL MEASURE THE EXPRESSION OF GENES IN SETS OF PUREBRED AND CROSSBRED EMBRYOS TO DETERMINE IF HETEROSIS OCCURS AT THE LEVEL OF GENE EXPRESSION. IF GENE EXPRESSION HETEROSIS DOES OCCUR, WE ARE ALSO INTERESTED IN UNDERSTANDING WHETHER IT OCCURS AT SPECIFIC GENES, ALL GENES, OR RANDOM GENES BETWEEN INDIVIDUALS. THIS PROJECT WILL ALLOW US TO OBSERVE GENE EXPRESSION HETEROSIS ON HUNDREDS OF CATTLE EMBRYOS IN THE CONTROLLED CONDITIONS OF A LAB. WE WILL ALSO IDENTIFY DNA VARIANTS THAT CHANGE THE EXPRESSION OF GENES IN THE DEVELOPING EMBRYO. FOLLOW-UP WORK USING MATURE ANIMALS WILL HELP US UNDERSTAND HOW MOLECULAR HETEROSIS CHANGES THROUGHOUT AN ANIMAL'S LIFE. WE EXPECT THAT UNDERSTANDING MOLECULAR HETEROSIS COULD HELP FUTURE CATTLE BREEDERS IDENTIFY INDIVIDUALS THAT WILL PRODUCE THE MOST EFFECTIVE CROSSES.