Page "Trichromacy" Paragraph 6

Their eyes include three different kinds of cones, each containing a different photopigment ( opsin ).

Their peak sensitivities lie in the blue ( short-wavelength S cones ), green ( medium-wavelength M cones ) and yellow-green ( long-wavelength L cones ) regions of the color spectrum.

( Schnapf et al, 1987 ).

S cones make up 5 – 10 % of the cones and form a regular mosaic.

Special bipolar and ganglion cells pass those signals from S cones and there is evidence that they have a separate signal pathway through the thalamus to the visual cortex as well.

On the other hand, these L and M cones are hard to distinguish by their shapes or other anatomical means – their opsins differ in only 15 out of 363 amino acids, so nobody has yet succeeded in producing specific antibodies to them.

But Mollon and Bowmaker did find that L cones and M cones are randomly distributed and are in equal numbers.