Why Are Wild Rats Brownish-Grey While Laboratory Rats Are White?

Is the rat in a laboratory, the one kept at home as a pet, and the one darting along city walls a different species? Not necessarily. Most often, they are… the same species: the brown rat (Rattus norvegicus).

What sets them apart—color, behavior, susceptibility to disease—is the result of domestication, selective breeding, and the conditions in which they live.

The Laboratory Rat – The Albino of the Lab

Since the 19th century, rats have been used in scientific research. Over time, laboratories began intentionally breeding rats with white coats—albinos. Why?

• They are easy to distinguish from wild rats,
• They have predictable genetic traits,
• The lack of pigment (albinism) is linked to a specific set of genes, which makes inheritance studies easier.

The white color results from a mutation in the tyrosinase gene, responsible for producing melanin—the pigment of the skin, eyes, and fur. As a result, albino rats have white fur and red eyes.

The Pet Rat – A Cousin With a Scientific Lineage

Most rats kept as pets come from laboratory lines. Thanks to breeding focused on appearance and sociability, many color varieties have emerged: white (albino), beige, chocolate, black, grey (husky), patched, spotted…

Unlike wild rats, whose fur color determines their survival, pet rats are bred for appearance and temperament.

The Wild Rat – A Master of Camouflage

The rats we see in cities, parks, and basements are still Rattus norvegicus, but in an undomesticated form. Their brownish-grey coloration is natural camouflage. It helps them blend into their surroundings and avoid predators.

White individuals in the wild stand no chance—they are too visible and often have poorer eyesight (albinos typically have vision defects). This is why white coloration can only persist in captive breeding conditions.

All of Them Deserve Protection

Although different at first glance, pet rats, laboratory rats, and wild rats are closely related. What separates them is the role humans have assigned them throughout history, but they share intelligence, social bonds, and remarkable adaptability.

For the Mushika Foundation, every animal—regardless of how society perceives it—deserves respect and protection.

Sources

1. Festing, M. F. W. (1979). Inbred Strains in Biomedical Research. Macmillan Press. 
2. Jacob, H. J. (1999). Functional genomics and rat models. Genome Research, 9(11), 1013–1016. https://doi.org/10.1101/gr.9.11.1013 
3. Hirashima, T., et al. (2005). Mutation in tyrosinase gene responsible for albinism in Wistar rats. Experimental Animals, 54(2), 157–162. https://doi.org/10.1538/expanim.54.157 
4. Hedrich, H. J. (Ed.). (2000). The Laboratory Rat, Volume I: Biology and Diseases. Academic Press. 
5. Animal Diversity Web (ADW). Rattus norvegicus (Brown rat). University of Michigan. https://animaldiversity.org/accounts/Rattus_norvegicus/ 
6. Animalia.bio. Brown rat (Rattus norvegicus). https://animalia.bio/brown-rat 
7. Wikipedia. Laboratory rat. https://en.wikipedia.org/wiki/Laboratory_rat 
8. PubMed Central (PMC). Albino rat genetics and tyrosinase mutation. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3420875/ 
9. National Center for Biotechnology Information (NCBI). Gene: TYR tyrosinase [Rattus norvegicus]. https://www.ncbi.nlm.nih.gov/gene/25562