What about animals that see more colors than humans?
What about all the scents a dog can smell and why humans can't? I want a dog nose! 😊
Or in other words, Johns Hopkins University has very poorly chosen a title for their article!
"... The findings ... increase understanding of color blindness, age-related vision loss, and other diseases linked to photoreceptor cells. They also demonstrate how genes instruct the human retina to make specific color-sensing cells, a process scientists thought was controlled by thyroid hormones.
By tweaking the cellular properties of the organoids, the research team found that a molecule derived from vitamin A called retinoic acid determines whether a cone will specialize in sensing red or green light. Only humans with normal vision and closely related primates develop the red sensor. ...
Instead, the new findings suggest red cones materialize through a specific sequence of events orchestrated by retinoic acid within the eye. ..."
Instead, the new findings suggest red cones materialize through a specific sequence of events orchestrated by retinoic acid within the eye. ..."
From the abstract:
"Trichromacy is unique to primates among placental mammals, enabled by blue (short/S), green (medium/M), and red (long/L) cones. In humans, great apes, and Old World monkeys, cones make a poorly understood choice between M and L cone subtype fates. To determine mechanisms specifying M and L cones, we developed an approach to visualize expression of the highly similar M- and L-opsin mRNAs. M-opsin was observed before L-opsin expression during early human eye development, suggesting that M cones are generated before L cones. In adult human tissue, the early-developing central retina contained a mix of M and L cones compared to the late-developing peripheral region, which contained a high proportion of L cones. Retinoic acid (RA)-synthesizing enzymes are highly expressed early in retinal development. High RA signaling early was sufficient to promote M cone fate and suppress L cone fate in retinal organoids. Across a human population sample, natural variation in the ratios of M and L cone subtypes was associated with a noncoding polymorphism in the NR2F2 gene, a mediator of RA signaling. Our data suggest that RA promotes M cone fate early in development to generate the pattern of M and L cones across the human retina."
Fig 1. An in situ hybridization approach distinguishes M-opsin and L-opsin mRNA.
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