Great article on egg colour

I came across this article on the Marans Club of America site-i thought it a good read and thought i would share.

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good stuff but a bit out of date - I believe that the latest research says there are at least 13 different gene loci involved in brown egg colour.

i think a few of her sources were from 2012 articles...so i guess it is outdated...but it is all news to me. If you have better info..i would love to read it. This is a new are of interest for me

It's sometimes hard to tell from the publication date when the original research was done. A 2012 article could cite original sources dating back 80 years or more (as that one did; Punnet is long dead), and there could easily be original research dating from, say, 2010 that was missed in a 2012 article. The "13 or more loci" estimate for brown egg colour has been around for quite a few years I think.

Review articles are very useful, in that they summarise stuff over many years or decades, but don't necessarily catch every development.

I'll see what I can find.

The bottom line is that blue egg colour is simple (one locus, blue is dominant allele; either you have it (one or two copies) or you don't. White eggs are a result of no blue or brown genes (or can also be a result of an eggshell colour-inhibiting gene that is sex-linked). Brown eggs are polygenic; i.e. under the influence of a number of gene loci (some with more influence than others). As the article points out, green is simply blue + brown.

Most traits (in people, chickens, dogs, everything) are polygenic. These are harder to breed for in the sense of getting them "fixed", or invariant in the population. Many (but not all) of the traits that define breeds are single locus traits - e.g. yellow vs white legs, pea comb, rose comb, etc.

ipf wrote:The bottom line is that blue egg colour is simple (one locus, blue is dominant allele; either you have it (one or two copies) or you don't.  

I really dislike this approach because it gives the wrong impression on how to work with the colour. While one gene may turn the blue colour on or off, the blue colour is just like the brown colour in that it's tone and intensity is influenced by several genes. In essense, one would use the same principles whether selecting for brown eggs or blue ones.

Yes, of course it's more complicated than it looks at first glance (pretty much everything is!), and there are clearly modifiers, I agree. But still, blue (in its basic manifestation) is clearly simpler in its inheritance mechanism than brown. Understanding the simple part is the first step, and one can then add on the wrinkles.

why would one look at the blue supressor gene any differently than the brown supressor gene? You can have the brown gene turned on and still select for white eggs just like a bird with the blue gene turned on can lay white eggs. Both are functionally the same.

It seems to be generally agreed that there are more loci affecting brown egg colour than blue, and that it's easier to get rid of blue than it is to get rid of brown, but you're welcome to your opinion.

the blue colour is just like the brown colour in that it's tone and intensity is influenced by several genes

Isn't the blue color from the hens ability to break down the pigment from the recycled Red Blood Cells. I venous blood is blue when de-oxygenated. De-oxygenation causes the RBC molecule to change shape and refract light at on different wave length-thus we see blue.
but where does the blue pigment come from?

No, the blue isn't just like the brown. There is one main gene locus (O/o); if you don't have the dominant allele (O), either homo-or heterozygous, you won't get blue or green eggs. There are other modifying loci, but without an "O" you won't get blue eggs.

With brown there are a moderate number of loci of small to medium effect - you can have a subset of them and get brown eggs. There is no single brown gene that is essential for brown eggs.

The chemical responsible for brown egg colour is protoporphyrin, an intermediate in heme synthesis.

The blue egg chemical is biliverdin, a breakdown product of hemoglobin. Biliverdin of egg shells is produced from the shell gland, rather than from the breakdown of erythrocytes in the blood stream.

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ipf wrote:No, the blue isn't just like the brown. There is one main gene locus (O/o); if you don't have the dominant allele (O), either homo-or heterozygous, you won't get blue or green eggs. There are other modifying loci, but without an "O" you won't get blue eggs.

and brown eggs are dependant on the brown suppression gene being absent. Again, I ask, what is the difference? Both colours are subject to a single on/off gene and subsequent expression is due to the cumulative effects of multiple modifier genes.

[quote="It seems to be generally agreed that there are more loci affecting brown egg colour than blue"]

and this agreement is based upon what research into blue egg modifying genes?

While there is much research into the genetics of brown eggshell colour, I'm not aware of the blue eggshell trait enjoying the same scrutiny.

(Actually there's some great new-ish research into the main blue egg gene, which is apparently a result of a retrovirus incorporating itself into the chicken genome. This happened not just once, but on two separate occasions, in two different spots on the genome, once in Asia and once in South America.)

My point is: to have blue eggs, you need at least one copy of the O allele. There is not a single gene/allele whose presence is absolutely necessary for brown eggs; they can result from many combinations. To me this is a real difference.

It is relatively easy to remove the O gene (and thus all blue egg tints) from your flock, while it is pretty hard to get out the brown. Sure you can use the sex-linked pr gene to remove the brown colour from your eggs, but all those underlying brown genes will still be lurking in your genome, just waiting for a chance to express.

The pr gene (according to Crawford) also reduces production, both in terms of egg number and size.

you still did not answer the question about research measuring the number of blue egg modifiers at play. That was the context of my previous question. Let's try to keep this an "apples vs apples" discussion instead of doing the "apples vs oranges" game.

"Sure you can use the sex-linked pr gene to remove the brown colour from your eggs, but all those underlying brown genes will still be lurking in your genome, just waiting for a chance to express."


and the same can be said for the O gene. removing the trigger gene does not remove the modifiers. Blue egg modifiers are found throughout the chicken genepool, they are not limited to the blue egg breeds. Your failure to make this basic intuitive connection is why I don't like the way the two traits are treated differently. And you are smart and very knowledgeable in this field, someone without the academic training is even far less capable of arriving at a correct practical conclusion.


The academic dogma has chosen to approach the two genes differently in how it represents their significance. However, this must have been decided upon via incomplete field experience because the logic fails when applied practically. This is a case where the academic dogma is a square peg trying to be forced into a round hole. It doesn't work as well as it could. But which should serve which? Should those working in the field be forced to adjust their practical applications to fit a faulty model? Or is it not more appropriate for the academic model to be adjusted to better fit the practical applications?

Does the tail wag the dog, or the dog wag the tail?

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A hot topic. Here is a picture taken at the latest scientific symposium on the matter.

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Fowler wrote:A hot topic.  Here is a picture taken at the latest scientific symposium on the matter.

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Looks like a lot of chicken fanciers there!

Indeed, you get the same thing at any general meeting.

Here is a fellow trying to submit a new colour of Plymouth Rock to the APA for breed recognition.
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Wow, Fowler! I can't imagine the chaos if someone was actually trying to have a new breed recognized!

Wait! That guy on the right! Isn't that Rico?