Final answer:
A mouse with a gene inactivated is known as a knockout mouse, which is different from transgenic or wild-type mice and is instrumental for genetic research.
Step-by-step explanation:
A mouse with one of its genes inactivated is referred to as a knockout mouse. This term denotes that a specific gene has been deliberately disrupted or 'knocked out' to study the gene's function or related biological processes. Unlike transgenic mice, which have new genes added to their genome, knockout mice have had genes turned off.
This research technique is a powerful tool in genetics and helps scientists understand genetic contributions to diseases and development. Wild-type mice, by contrast, are those with no deliberate genetic modifications, possessing the natural form of genes found in the species. The process of creating knockout mice is an essential aspect of reverse genetics, allowing researchers to observe how mutations affect an organism's phenotype and consequently infer the function of the gene.