Why are inbred strains preferred when creating transgenic mice?

• A. Inbred strains are easier to maintain in colonies.
• B. Inbred strains have uniform phenotypes so differences are easier to see.
• C. Inbred strains have greater reproductive efficiency.
• D. Inbred strains have more chromosomes so it's easier to integrate an extra transgene.

Answer: (B)

The main idea is that genetic background uniformity makes it easier to see the effects of a transgene. Inbred strains are bred for many generations to be genetically almost identical, so differences you observe between a transgenic mouse and its control are more likely due to the transgene itself rather than other genetic variation. This leads to clearer, more interpretable results and improves reproducibility between experiments because the background genetics don’t introduce extra variation. If you used a genetically diverse (outbred) strain, natural variation could mask or confound the transgene’s effects, making it harder to attribute outcomes to the transgene and often requiring larger sample sizes.

Other choices aren’t the main reason. Maintenance ease is not the driving factor for selecting inbred strains in this context. Reproductive efficiency can vary and is not consistently better in inbred lines. All mice have the same chromosome count, and having more chromosomes does not make transgene integration easier.