Describes the discovery of a LINE-1 element, L1C105, in the Mus musculus domesticus inbred strain, C57BL/6J, which was found to belong to a M. spretus LINE-1 subfamily originating within the last 0.2 million years. Cloning of L1C105; Sequence of L1C105; L1C105 and L1EL111 as belonging to different M. spretus LINE-1 subfamilies.