The function of the animal core is to provide services in many aspects of this program project, including Projects 1, 2, 4, and 5. First, it will supply the animals which produce fertilized ovum and foster mothers for transgenic experiments. It will also provide ES cells and blastocysts for the homologous recombination experiments. It will monitor the quality of the ES cells used and maintain the transgenic and homologous recombination mouse lines and breed the different lines to homozygosity in order to create a mouse model which carries human sickle hemoglobin as the predominant adult hemoglobin. It will maintain these animals and provide them to other investigators for testing of pharmacological agents.