Why are laboratory rats white? - briefly
Laboratory rats are albino, bred specifically for a lack of melanin, which produces a white coat and simplifies visual tracking in experiments. The uniform coloration also reduces genetic and phenotypic variability, improving experimental consistency.
Why are laboratory rats white? - in detail
Laboratory rodents are predominantly white because most strains are derived from the albino mutation of the Norway rat (Rattus norvegicus). The albino phenotype results from a recessive allele (c) that disables melanin production in melanocytes, leading to a lack of pigmentation in the skin, hair, and eyes. Breeders maintain homozygosity for this allele (c/c) to ensure uniform coloration across colonies.
The white coat offers practical advantages for scientific work. Uniform coloration simplifies visual assessment of physiological changes, such as wound healing, tumor growth, or skin lesions, by providing a neutral background that does not obscure measurements. It also facilitates automated image analysis, where contrast between the animal and its environment improves detection accuracy.
Historically, the first albino rats entered research laboratories in the early 20th century. Selective breeding programs quickly expanded the population, establishing inbred lines such as Sprague‑Dawley, Wistar, and Fisher 344. These lines combine the albino trait with other genetically defined characteristics (e.g., specific disease susceptibilities, growth rates), creating standardized models for reproducibility.
Genetically, the albino mutation is located on chromosome 5 and affects the tyrosinase gene, which encodes an enzyme essential for converting tyrosine to melanin. Loss‑of‑function mutations in this gene halt the melanin synthesis pathway, producing the characteristic white phenotype and pink eyes due to visible blood vessels.
Additional reasons for the prevalence of white laboratory rats include:
- Ease of breeding: Albino rats have high fertility and robust litter sizes, supporting large colonies.
- Reduced variability: Consistent coat color minimizes phenotypic variation unrelated to experimental interventions.
- Historical inertia: Established protocols, equipment, and data sets are built around albino strains, discouraging the adoption of pigmented alternatives.
In summary, the dominance of white laboratory rats stems from a recessive albino mutation that eliminates pigmentation, combined with breeding practices that prioritize uniformity, experimental visibility, and reproducibility.