Transgenic mice are genetically modified animals that have been created by introducing a foreign gene into their DNA. This can be done using techniques such as gene transfer or gene splicing, and is often used in scientific research to study specific biological processes or diseases. The term "transgenic" refers to the fact that the introduced genetic material comes from another species - this could be a different animal species (such as introducing human DNA into a mouse), or even from a different kingdom of life, such as bacteria or plants. Transgenic mice are often used in biomedical research because they can provide valuable insights into the function and behavior of specific genes, and can serve as models for studying diseases that affect humans.