What determines eye color in rats? - briefly
Rat eye coloration is controlled primarily by the amount and type of «melanin» produced in the iris, regulated by genes such as Tyrp1 and the albino (Tyrc) locus. Mutations that diminish melanin synthesis produce pink or red eyes, whereas functional alleles yield brown or black pigmentation.
What determines eye color in rats? - in detail
Eye pigmentation in rats results from the synthesis, transport, and deposition of melanin within the iris. Production of the pigment relies on the enzymatic activity of tyrosinase, which converts tyrosine to dopaquinone, the precursor of both eumelanin (dark brown/black) and pheomelanin (red‑yellow). The relative balance of these melanin types determines the observable hue.
Genetic variation governs the presence and activity of the enzymes and transport proteins involved. Mutations that reduce or eliminate tyrosinase function generate albinism, leading to pink or red‑appearing eyes due to the visibility of underlying blood vessels. Other loci influencing ocular color include:
- Oca2 – controls melanosome maturation; loss‑of‑function alleles produce reduced melanin and lighter eye color.
- Tyrp1 – modulates melanin polymerization; altered alleles shift the eumelanin/pheomelanin ratio.
- Mitf – transcription factor regulating expression of pigment‑related genes; hypomorphic variants decrease overall pigment production.
- Gpnmb – affects melanosome formation; defective alleles associate with diluted eye pigmentation.
These genes often exhibit pleiotropy, linking eye coloration to coat color phenotypes. Inbred laboratory strains illustrate the effect: the albino strain (e.g., Sprague‑Dawley) carries a null mutation in the tyrosinase gene, whereas pigmented strains (e.g., Brown Norway) retain functional alleles at the aforementioned loci, resulting in dark brown eyes.
Environmental factors have minimal impact on ocular hue; melanin synthesis is intrinsic to cellular metabolism and is not substantially altered by diet or lighting conditions. Consequently, the observable eye color of a rat serves as a reliable phenotypic marker of its underlying genotype.