Ameraucana color question

[sugarbush]

Quote:
Search egg shell genetics on ebscohost or infotrack. there are hundreds of scientific articles on the topic. You will have to go to your local college library to gain access or pay for a subscription to either electronic database.

One of the limitations to the internet is there are very few actual scientific journals online.....They protect their research by charging for access.

I am married to a human geneticist, so I have a more than average knowlege of genetics. Those who believe that egg color genes can "overlay" eachother are violating Mendel's law... Codominant genes exist in poultry, but not when it comes to egg color.

 

[hbarn]

Thanks for the suggestions on where to start the search for information on egg color genetics. It does sound more like coat color genetics if I understand what Sonoran Silkies wrote that there are 12 genes affecting shell color, with basic brown or white being the two main types with blue an uncommon (genetically) third, but they can be modified by genes altering shade or even coatings affecting the appearance of the color. I,ll try and do some searching to find if there are some scientific documents explaining the dominance of the egg color genes.

It is fun to have such variables in the expression of shell color, always a surprise!

 

[Sonoran Silkies]

I think you misunderstood. There are 2 colours of eggshells: blue and white. There are another 12+ genes that affect any coating applied to the surface of the shell. Brown is essentially painted onto the white or blue shell.

 

[sugarbush]

Yes and the blue genes are thought to have been bred in at some point by crossing chickens with pheasants. Usually brown coatings go with white egg color. Lighter brown coatings result in what is sometimes called pink eggs. Greens are just light color blue and some blue eggs are actually white eggs with a coating that makes it look blue. A hen that lays a true blue egg will have offspring that lay a blue egg which is why blue egg layers have been crossed with high production white lines like leghorn....it makes a higher production chicken that lays a blue egg. Blue egg gene is autosomal dominant so it only takes one copy from either parent to make the offspring lay a blue egg....

 

[Krys109uk]

Interesting.....Is the chicken X pheasant a theory or has it been demonstrated?

I don't think anyone is trying to say that egg colour genes are codominant; I don't think anyone is saying O is an allele to any of the brown colour genes.

Please clarify...The blue or green eggs you mention (presumably chicken eggs) which are coatings rather than blue through the shell..... Presumably these are caused by gene(s) other than O?

Green eggs would often seem to be blue eggs with a coating......If one cracks a green chicken egg & picks the membrane off the inside, the shell is often much more blue in colour.

.

 

[sugarbush]

The pheasantX blue egg allele is a theory based on the fact that blue is not effected by the alleles that effect white eggs and make them appear brown or pinkish. That suggests that it came from a species other than chicken. I imagine at somepoint somebody somewhere will get the financial backing to run the genome and prove the theory right or wrong.

Blue and white are not that far off of eachother in the color spectum. I have often seen cream eggs that almost looked blue. The gene for a blue egg is dominant over the white and with the many reports people make about having a chicken hatched from a blue egg lay a white egg the only explanations would be that the blue egg only looked blue.

It was suggested earlier in this thread that this cross and that cross results in one gene "overlaying" another and a resulting in a different color egg in the offspring. That general statement implys that breeding for color is like mixing paint..... That is why I brought up the eye color example that then everybody went of on a frenzy about blue and brown making hazel...... I guess what I thought was a very simple example was too complicated for some... Egg genes are not codominant like the genes of a carnation....so mixing colors does not result in other colors...that is a violation of Mendel's law. It was also suggested that "original" Araucana layed blue eggs and that hatcheries bred for the range of color....That theory is also disproven by the dominance of the blue egg.

All right....to sum up the history of the araucana as we know it. The rumplessness was introduced to south american flock by the Dutch when they brought Pursian Rumpless with them during the colonial period. The native tribes liked the rumplessness because they believed it help the chickens avoid preditors so they bred it into their mixed breed flocks.

Dr Ruben Bustros then selectively bred for blue eggs, rumplessness, and cheek tufts and then the chickens he selectivey bred were presented to the world poultry congress as a naturally occuring breed. (not selectively bred) Dr Bustros birds never made it to the United States. The birds that where imported here were the mixed breed chickens that the Araucana kept in their flocks. They could be rumpless, tailed, tufted, bearded, lay blue or other colored eggs etc. Breeders here called them all Araucana chickens as did the hatcheries.

Then when breeders wanted the APA accept the standard for Araucana they brought their birds and the APA, and based on the reports that where made at the WPC in 1918, the APA rejected the standard that the breeders wanted and implimented the standard of Dr Bustros selectively bred birds which at the time the APA thought were pure bred and naturally occuring. None of the birds brought before the APA as examples qualified as araucana by the new standard....they where rumpless and tailed, layed multi-colored eggs had beards etc. The breeders continued to breed their birds and started calling them American Aruacana which was later shortened to Ameraucana. This history is why I have no problem with people still calling an EE or Ameraucana an Araucana. It was the mis-information of the APA that made this into such a mess and they took a bird that even Bustros didn't call an Arucana and attached that name to it, making the birds that were rightfully Araucana into something else. Then a new generation of breeders sprouted out and they selectively reproduced the birds that Bustros did from the stock that now are looked down on by them as mutts and unfit for show; what is now commonly called an EE.

 

[Krys109uk]

There is obviously quite a lot involved in egg colour. Generally speaking I'd agree that genetics is not just like mixing paint. But, in the question of egg colour, to a certain extent, I think it could be described a bit like that.

First, take for instance the Marans which is dark egg laying breed. One can actually wash the brown off many of these eggs leaving a light brown underneath. When bred with a homozygous O//O bird, the offspring will be O//o+ & heterozgous for some of the brown egg coating genes from other loci which it would have inherited from the Marans. The result is a dark green/olive green egg. This egg does not hve an olive green shell right through & if one cracks the egg & looks under the membrane the egg shell will be blue. That's just the way it is. That shell isn't olive right through; basically it has the appearance that someone has taken a blue egg & spray painted brown paint onto it. One cannot always wash off all brown pigment but in the case of very many of the extra dark egg layers it is caused by a blood pigment being laid over the egg shell after it laves the shell gland & on it way to being laid.

Nobody is implying that chicken eggshell colour has anything to do with codominance. Mendel's pink carnations also did not show 'codominance' they expressed 'incomplete dominance' . Codominance is when the traits of both alleles in the heterozgote are expressed. Incomplete dominance is when the heterozygote is expressed as an intermediate.

A female hen which hatched out of a blue egg but does not, itself, lay a blue egg has a simple explanation which comply with Mendelian principles.....the mother was heterozygous for O//o+ & the female offspring inherited the recessive o+ from the mother & another o+ from the father.

I hope this clarifies to some extent.

As a point of interest.... The Shetland Chickens make interesting reading, but I think their history is probably rather vague. Many of these chickens were/are blue egg layers; their ancestry is thought to have gone back to the Vikings.

 

[Sonoran Silkies]

First, some terminology:

Gene--A piece of DNA located at a specific locus on the chromosome.

Allele--alternative genetic expression for a specific gene. The alleles for andalusian blue are Bl & bl; the alleles for columbian are Co & co; the alleles for black are E, E^R, E^Wh, e+ & e^b; the alleles for recessive white are C, c, c^re, c^a; etc.

Dominant--A single copy of the allele will cause the trait to express, regardless of another allele's presence in the organism. There is no obvious difference between a heterozygote and a homozygote. Examples would be Co, Fm, Mh, O, R.

Incompletely Dominant--A double copy of the allele results in complete expression of the trait, whereas a single copy of the allele results in an intermediate expression of the trait. Examples would be Bl, Di, F, I, Ml, S.

Recessive--The trait is expressed only when no other allele is present in the organism. Examples would be lav, choc, c, h, ig, lav, mo, w.


The pheasant theory is just that, a theory, and I believe it is generally discounted by modern studies. I am not as well versed in this as in some other areas.

There was absolutely no mention of genetic "overlay," although I can see how the phrasing of the original comment might have suggested it.

That is because one color is over the other.

However many subsequent comment by that person, myself and others clearly stated that the genes that cause brown pigment are not IN the eggshell, but are applied as a coating to the egg's surface.


A hen can be heterozygous for O (the blue eggshell gene). This means that genetically she is Oo, and that only half her progeny will receive O; the other half will receive o.

If mated to a homozygous male (OO), all offspring will receive O from him, and will have at least one copy of the blue egg gene; the females will lay blue eggs.

However, if he is homozygous for not-blue-egg (oo) he will pass that trait to all his offspring. Only the ones who receive O from the hen will lay blue eggs and be capable of passing the trait to their offspring. The ones who receive o will lay white eggs, which may or may not be covered by a layer of brown pigment, depending on the other egg colour genes.

To quote from a respected poultry geneticist from another website, "Brown eggshell is a complicated trait and as many 13-14 genes have been proposed to explain the inheritance of the trait. "


As for history and development of the breeds, please check out the references I listed earlier:

You can read more about the history of these breeds and their development at http://ameraucana.org/history.html Another very good pair of articles on both araucanas and ameraucanas is at http://www.araucana.net/images/ACA_Images/Araucana_Alan_Stanford_Article.pdf​

 

[Solsken Farm]

Thank you Sonoran! That is helpful to a genetic neophyte such as myself.

 

[Sonoran Silkies]

You're welcome