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.
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.