of color is dependent on having a color sensor
, we have three kinds of color sensors, or cone photopigments
, one each for red
. About 8% of men
who are color-blind
typically have the cone for blue, and are missing either the green or red cones. Sometimes they will have cones that see two very slightly different red or green hues. This is possible because there are a number of genes
that code for each of the red, green and blue cone photopigments. Thus not everyone has the same set of red, green and blue cones.
This suggests that not everyone has the same perception of color.
The genes for the red and green photopigments are adjacent to each other on the X chromosome; blue however is on another chromosome. Women, of course, have two X chromosomes and therefore two sets of red and green photopigment genes. Men have only one X, so they have just one shot at getting the red and green photopigment genes right. This is why color blindness occurs mostly in men.
Because the genes for the red and green photopigments are right next to each other, those genes sometimes mix, and every once in awhile one of five bad combinations of the genes that code for the red and green cone photopigments can occur.
The X chromosome is missing either a red or a green photopigment gene.
The X chromosome has two identical red photopigment genes instead of both red and green ones.
The X chromosome has two slightly different red photopigment genes.
The X chromosome has two identical green photopigment genes.
The X chromosome has two slightly different green photopigment genes.
In each of the above cases the man will be color blind.
Now the interesting thing about this is that women have two sets of X chromosomes. So there is a possiblity that instead of having just three types of they may have four types cone photopigments. One X chromosome has the normal complement of red and green photopigment genes, the other has a differrent set of genes for either the red or green cone photopigments. This would very likely give her enhanced color vision.