Researchers have identified a gene in humans that (when mutated) causes tremors and unstable walking due to neurological problems. This disorder is inherited in an autosomal recessive manner, and the mutant allele is known to result from a loss-of-function mutation. The same gene has been found in mice, although a mutant mouse version has not been discovered. To develop an effective drug therapy to treat this disorder in humans, it would be experimentally useful to have a mouse model. In other words, it would be desirable to develop a strain of mice that carry the mutant allele in the homozygous condition. How would you develop such a strain?