eye color

Floyd Waddle fwaddle at CHI1.UNCFSU.EDU
Wed Dec 11 20:29:18 EST 1996

The short answer to the question of what will brown X green produce? is 
Just about anything. The long answer is that eye color genetics in humans 
is not well described in the textbooks. The older books claim brown is 
dominant to blue which isn't true.  The reason is that blue is not the 
genetic alternative to brown. Brown eyes is due to the presence of 
melanin in either the front half of the iris or the entire iris - the 
literature I've read is confusing here.  Whichever it is, the genetic 
alternative may be "presence of melanin" (dominant) vs "absence of 
melanin" (recessive). Moreover there are two types of melanin, eumelanin 
and phaomelanin.  In mammalian hair, eumelanin produces black and brown, 
phaomelanin produces yellow.  Lack of melanin produces blue eyes due to 
light refraction. Presence of melanin produces green to dark brown.  
(Green = yellow + blue) If this explanation is true so far, then the 
actual eye color of pigmented eyes is controlled by modifier genes which 
determine amount and placement of pigment. I suspect the full explanation 
is somewhat different than this since this does not account for dark vs 
light blue eyes.  If you check enough biology and genetics textbooks, you 
might find a better explanation.  This at least accounts for why a green 
eyed person and a blue eyed person can have a brown eyed child. The blue 
eyed person cannot express genes that determine how much melanin is 
present, but can pass such genes on to offspring.

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