How did white rats appear? - briefly
White rats originated from albino mutations in wild Norway rats that were isolated and selectively bred to produce a stable, fully white laboratory strain in the early 20th century. Their uniform coloration and lack of pigment made them ideal for scientific research, leading to widespread use worldwide.
How did white rats appear? - in detail
White laboratory rats with a pure white coat and pink eyes are the result of selective breeding that began in the early 20th century. The process involved several key steps:
- Identification of naturally occurring albino individuals among wild‑type brown rats (Rattus norvegicus).
- Cross‑breeding of albino founders with standard laboratory strains to introduce the mutation into a genetically uniform background.
- Repeated backcrossing to eliminate unwanted traits while preserving the albino allele, which is recessive and located on chromosome 14.
- Establishment of closed colonies that maintained homozygosity for the albino gene, ensuring consistent phenotype across generations.
The first documented albino rat colony was created by William Castle in 1905 at the University of Cambridge. Castle isolated an albino pup and bred it with a brown rat, then selected offspring that carried the albino allele. Over successive generations, the white coat became fixed, and the strain was distributed to other research institutions.
Genetically, the albino phenotype arises from a loss‑of‑function mutation in the tyrosinase (TYR) gene, which blocks melanin synthesis. Homozygous mutants lack pigment in skin, fur, and eyes, producing the characteristic pink ocular appearance due to visible blood vessels.
Commercial production of white rats expanded after the 1920s, when the Carnegie Institution and other laboratories standardized the strain for pharmacological and physiological studies. The resulting animals, often referred to as “Wistar” or “Sprague‑Dawley” white rats, combined the albino trait with selected characteristics such as rapid growth, docile behavior, and reproducible disease models.
In summary, white rats emerged through identification of a natural albino mutation, systematic introgression into laboratory lines, and rigorous inbreeding to achieve a stable, homozygous population used worldwide for scientific research.