As I understand it, the Catholic Church has held that genetic engineering, with the intent to play God, or to “improve” on His creation, is immoral. However, genetic engineering can be moral if its objective is to assist in God’s original plan, and the methods and goals preserve a fundamental respect for human dignity. Thus, it may be morally defensible to remove the extra chromosomes of 21-trisomy (Down’s Syndrome) patients in the same way as it is permissible to cure someone of any other condition. However, it is not permissible to create “designer” babies who will have the desired sex, height, IQ, etc. Similarly impermissible is the combining of animal with human genes, to create animal-human hybrids, or to otherwise design humans with “unique” abilities. Any genetic engineering must be oriented toward the healing of a particular patient, and not some impersonal eugenics program or the like.