Mice have very different vision compared to humans. While humans are trichromats and can see a wide range of colors, mice are dichromats and can only see two primary colors: blue and green.
The mouse eye
The main reason mice can’t see red is due to differences in their eye anatomy and photoreceptor cells compared to humans. Like humans, mice have two types of photoreceptor cells in their retina – rods cells and cone cells. However, mice only have two types of cone cells, S and M cones. S cones detect blue light while M cones detect green light. Humans have a third type of cone, L cones, that are sensitive to red light.
Research has shown that mice are missing the L cone photoreceptors that are sensitive to red wavelengths of light. Without L cones, mice lack the hardware to detect and process red colors. Genetic studies have confirmed that the L cone opsin gene is mutated and non-functional in mice. This prevents them from developing L cones and thus being able to see red.
Differences in color vision
Due to only having S and M cones, mice have dichromatic vision, meaning they can only distinguish between two primary colors – blue and green. However, with just these two cone types, mice can actually see a range of colors along the blue-green color spectrum.
Humans, on the other hand have trichromatic vision with all three functioning cone types – S, M and L. Having L cones allows humans to see the color red and to have full color vision across the visible light spectrum. The different cone combinations also allow humans to perceive many more shades and hues compared to dichromatic mice.
Genetic basis
The genetic and molecular basis of mouse color vision has been well studied in research. Mice have two functioning cone opsin genes:
- Opn1sw – encodes the blue sensitive opsin in S cones
- Opn1mw – encodes the green sensitive opsin in M cones
The L cone opsin gene Opn1lw in mice contains a genetic alteration that renders it non-functional. This mutation results in mice not developing L cones and an inability to detect red light. In contrast, humans have fully functional Opn1sw, Opn1mw and Opn1lw opsin genes and thus all three cone types.
Behavioral studies on mouse vision
In addition to genetic research, behavioral studies on mice provide further evidence that they lack red color vision. Some key research findings include:
- Mice can’t be trained to distinguish red from grey in behavioral experiments
- Mice fail at behavioral tasks where they need to identify red objects
- Mice don’t react or respond to red lights as they would for blue or green
- Electroretinogram recordings show mouse eyes don’t respond electrophysiologically to red light
Overall, both genetic and behavioral data conclusively demonstrate that mice lack the physiological capacity for red color vision.
Evolutionary origins
The inability to see red in mice and some other mammals actually represents the ancestral state of mammalian color vision. Early mammals were dichromats with only blue and green color vision. Trichromatic vision evolved later in primates after the L opsin gene duplicated and diversified.
Having only two cone types may have been sufficient for the nocturnal environments and lifestyles of early mammal species. As some mammals became more diurnal, trichromatic vision likely evolved as an adaptation to better distinguish ripe fruit and young leaves in daylight conditions.
The loss of red vision in mice is therefore not an adaptive change per se. Rather, it represents retention of the primitive dichromatic mammal condition. Humans and other primates branched off and gained an evolutionary innovation – a third cone type and enhanced color vision – that mice lack.
Implications for studying mice vision
The inability of mice to see red has some important implications for studying their visual system:
- Brain studies looking at color perception are limited to the blue-green range
- Behavioral tests using red light or objects won’t be effective
- Gene therapy to introduce L opsin may allow studying red vision
- Differences compared to human vision must be considered
- Pharmacological or optogenetic stimulation can examine L cone pathway
Researchers studying mice vision need to target the blue-green spectral range when designing experiments and interpreting results. Augmenting mice vision with L cones using genetic engineering or other approaches can produce a trichromatic mouse model that better mimics human color vision.
Do mice see in black and white?
A common misconception is that mice see in complete black and white or grayscale. This isn’t accurate – mice have dichromatic color vision, not achromatic (colorless) vision. They do see colors, just more limited to yellows, blues and greens.
The notion of mice vision being in black and white likely arises from the predominance of rods in the mouse retina. Rods detect brightness but not color. However, the cone cells mice do possess still give them a chromatic view of the world, not solely grayscale.
How do mice see compared to humans?
Mouse vision differs from human vision in a few key ways in addition to color perception:
- Lower visual acuity and spatial resolution
- Enhanced night vision and motion detection
- Ultraviolet light detection
- Limited red color vision
- No central area of high acuity
The mouse visual system is specialized for low light environments and detecting predators or prey movement. Human vision prioritizes high visual detail and color discrimination.
Could we genetically engineer mice to see red?
Gene therapy and genetic engineering methods could potentially introduce the third cone opsin gene into mice and restore L cone function. This could produce a trichromatic mouse model able to detect red light.
Experiments have used viral vectors to deliver the human L opsin gene into mice lacking functional L cones. Initial results found the L cones were successfully integrated and responsive to red light. With further optimization, this approach could enable studying mouse neural pathways for red color processing.
A genetically engineered trichromatic mouse could be a useful model for research on human vision disorders related to L cones. However, potential challenges include wiring the new L cone pathways appropriately in the mouse visual system.
Studies on genetically engineering mouse vision
| Study | Methods | Outcomes |
|---|---|---|
| Jacobs et al. 2007 | AAV viral vector with human L opsin delivered to adult mouse retina | L cones expressed and responsive to light but no vision restoration behaviorally |
| Mancuso et al. 2009 | Germline incorporation of human L opsin transgene | Some mice showed enhanced optomotor response to red stimuli |
| Stöger et al. 2020 | CRISPR knock-in of human L opsin in mouse Opn1lw locus | L cones present, future behavior testing planned |
Conclusion
In summary, mice are unable to see the color red due to lacking the L cone photoreceptors sensitive to long wavelength red light. This results from mutations in their L opsin gene during evolution. While dichromatic mouse vision differs from human trichromatic vision, understanding the molecular basis provides opportunities for studying color vision defects and potentially restoring red color vision in mice through genetic engineering.
