I assume it is the same reason that women have stripey skin.
at ~ 100 cells, if the embryo has 2 X chromosomes the cell shuts one of them off, which one is random, those cells continue to multiply bringing their specific X chromosome with them.
So women have genetically distinct blotches all over their body based on which cell disabled which X chromosome.
I will have to leave this one for the scientists but I assume tetracromats got some of their cone cells from X and the rest from X`
The implication being, I don't think tetracromats have some sort of super vision, they just have what would be considered color blind if all their color cells were defective. But because only some of them are they get an interesting subtle addition to their color sense.
There exists two genes that code for the red-cone-detector. They sense /slightly/ different shades of red (more precisely, their gaussian-like filters are centered differently).
And these are carried on the X chromosome. Either one or the other is in a male fertilized cell, but both are possible in a female fertilized cell.
The measurable end result is that some few women have both kinds of cones (therefore four color detectors, where two majorly overlap in the red region). These tetrachromats can detect finer distinctions between colors on the red end of the spectrum; their color detection in green/blue is identical to ordinary color vision.
at ~ 100 cells, if the embryo has 2 X chromosomes the cell shuts one of them off, which one is random, those cells continue to multiply bringing their specific X chromosome with them.
So women have genetically distinct blotches all over their body based on which cell disabled which X chromosome.
I will have to leave this one for the scientists but I assume tetracromats got some of their cone cells from X and the rest from X`
https://www.youtube.com/watch?v=BD6h-wDj7bw (veritasium: Why Women Are Stripey)
The implication being, I don't think tetracromats have some sort of super vision, they just have what would be considered color blind if all their color cells were defective. But because only some of them are they get an interesting subtle addition to their color sense.