genetics of eye coloration

[centrarchid]

My games typically have the red eye of American games but occasionally they throw offspring with dark eyes. Eye coloration does not appear to be linked to feather coloration. When I cross a red eyed game rooster (out of a dark eyed hen) with a red jungle fowl hen, three female offspring have dark brown eyes and while four brothers do not. At least one of pullets from same cross that is no longer had red eyes. Is eye coloration normally sex-linked on Z-chromosome?

 

[AquaEyes]

I don't know, but I'll be sure to be

 

[gallorojo]

There is some sex linkage involved, yes. I can't recall now where I read that, but, for sure it is there, and documented. For example, if you cross a melanized wheaten or partridge with a pure black, all the females will be dark eyed and dark face, "gypsy faced", while the males will not. Even if all parents had red eyes and red faces, the pullets will be gypsy faced. They will still have white or yellow skin. Let me see if I can dig up the documentation.

 

[gallorojo]

All I can find are some bits and pieces, but, most of the big genetics books discuss it. Seems there is some disagreements about how it all works, but, you are not the first to notice this. I've seen what you describe myself.

 

[centrarchid]

Quote:
Maybe more than one mechanism. I have just started making detailed observations on my birds. Records will be kept for a few generations to see how it works. Almost all the dark-eyed birds are females. Same bunch may have the pattern gene of red quill but lack black so hens are not proper red quill. Another person with genetics bent suggested my line at least at one time carried recessive black. Maybe the phenotypes are related?

 

[exop]

There are definitely a bunch of genes which affect eye color... I think there may be a carotenoid enhancer for one thing. I have 2 lines of Buckeyes and one has gold eyes with an orange tint from visible blood vessels in the iris, the other line has vivid orange eyes, verging on red which "fade out" when a hen has been on the lay for a long time. You can see some of the blood vessels in the iris with these birds as well, but the orange color seems to be evenly distributed and looks like a pigment to me.

The mottling gene mo also seems to affect eye color. Birds with mo/mo, mottled plumage, have a yellow or orange-gold tinted eye with no brown coloring; my black or blue birds which are Mo+/mo have a brown and gold tortoiseshell pattern in the iris which I haven't seen before.

 

[Chris09]

Genetics of eye color:

The genetic basis of eye color has not been extensively studied as have other aspects of phenotype. However, some things are accurately known. First of all, the wild-type eye is characterized by the Light Brown Leghorn. Eye color is a result of pigmentation of a number of structures within the eye (iris, retina, uveal tract, ciliary).

The bay-color eye (various shades of reddish brown) is due to carotenoid pigments and the blood supply of the iris. Brown eyes are increasingly melanized with the darkest eye color due to the fibromelanotic gene characterized by heavy eumelanin deposits throughout the eye. Little is known about pearl eye and Smyth has speculated that it has the same eumelanin distribution as the bay but without the carotenoids.

Eye color is modified by a number of genes that are known to be associated with shank and plumage color. The sex-linked dermal melanin genes, id+ and idM enhance dermal shank and eye pigmentation. The inhibitor of shank dermal melanin, Id, also inhibits eye pigmentation. Smyth hypothesized that the idM gene together with extended black, E, is responsible for dark brown eyes. idM also darkens the eye on the e+ background.

A dominant sex-linked inhibitor of eye pigmentation is known, Br. This trait is not useful for developing sexable day-old chicks because chickens do not get their final eye color until they reach sexual maturity.

In the absence of other melanin inhibitors, the E-locus alleles, E (extended black) and ER, birchen, result in a brownish eye with the E allele making the darker eye. Sex-linked barring, B, and eumelanin inhibitors at the E-locus, like eWh have an effect on eye color. Recessive white seems to have no effect on eye color and dominant white, I, has a strong ability to inhibit eye pigmentation. The genetics of pearl are not known, however, it is known that the white skin gene, W, is not the genetic basis of pearl eye, since Cornish have yellow skin and can also have pearl eye

Above From http://sellers.kippenjungle.nl/page2.html

Chris

 

[centrarchid]

Quote:
Thanks Chris,

Give me time to digest. Based on first read and limited observations I am dealing with the sex-linked idM. Wild-type feather coloration at E-locus can be dark eyed while full-sibling with the "birchen" or pattern gene as operating in red quill does not show dark eyes, at least not in heterozygous form.

 

[tadkerson]

idM is Massachusetts dermal melanin (allele to id+, Id and other alleles) This mutation is expressed in day old chicks- others are not expressed in day old chicks.

Tim

 

[centrarchid]

Quote:
Tim,

I failed to photograph these guys at hatch. Will have to repeat matings next year to see again. Do males have to have two copies of idM to exhibit dark eyes. Not a single of my males has dark eyes at this time.

Jim