This legislation, known as the Human-Animal Chimera Prohibition Act of 2025 , aims to amend title 18 of the United States Code by establishing a new chapter to prohibit certain types of human-animal chimeras. The bill provides a comprehensive definition of a "prohibited human-animal chimera," encompassing various scenarios such as human embryos with nonhuman cells that make their species membership uncertain, embryos resulting from the fertilization of human eggs with nonhuman sperm or vice versa, and embryos containing haploid sets of chromosomes from both human and nonhuman life forms. It also includes nonhuman life forms engineered to develop human gametes, brains, or facial features. The Act makes it unlawful for any person to knowingly create, attempt to create, transfer, transport, or receive these prohibited human-animal chimeras in or affecting interstate commerce. It also specifically prohibits transferring a human embryo into a nonhuman womb or a nonhuman embryo into a human womb. Violators face severe penalties, including imprisonment for up to 10 years and substantial fines, with additional civil penalties for those who derive pecuniary gain from such violations. However, the bill clarifies that it does not prohibit research involving transgenic animal models containing human genes or the transplantation of human organs, tissues, or cells into recipient animals, provided these activities do not fall under the explicitly prohibited categories.