why do some chickens lay blue eggs

Growing up in New England, PI lived across the street from my grandparents chicken farm. I am not sure which
they raised, so I don t know about the different colored chicken eggs they had. PFrom photos I ve seen, they looked to have a flock mostly consisting of and Australorps. Both are brown egg-layers. Around our house, we knew the saying brown eggs are local eggs and local eggs are fresh. I knew that there were brown chicken eggs (from our grandparent s farm) and white chicken eggs (from the supermarket). It wasn t until I dove back into backyard chicken keeping as an adult several years ago that I learned as well as which chickensPlay blue eggs, green eggs, and even pink eggs. I now raise many chicken breedsPand love having a colorful basket made up of the different eggs collected from them. Since I was interested in finding out WHY different eggs are different colors, I have done a bit of research into what exactly causes this. It s actually pretty fascinating stuff! P All chicken eggs start out with white shells made primarily of calcium carbonate. No matter what breed the chicken or what color an egg ultimately ends up being, all eggshells begin as white. The white egg-laying breeds, including Leghorns, Andalusians, Catalanas, Lakenvelders among others, don t possess any pigment genes, so they lay white eggs. Because Leghorns were specifically bred to eat little and lay a lot, they were the darling of the commercial egg industry and thus the reason why most store-bought eggs were primarily white P until recently. The perception that brown eggs are fresher and more nutritious (neither true, by the way! ) has led to the introduction of brown eggs to grocery store chains in recent years.


The brown egg layers such as Rhode Island and New Hampshire Reds, Australorps, Buff Orpingtons, Delawares, Brahmas and Plymouth Rocks, possess brown pigment genes and a brown dye is applied (by the hen of course! ) to the eggshell fairly late in the laying process; around the last 4-6 hours of the total 26 hours it takes to form the egg. This results in a brown-shelled egg. Interestingly, the inside of a brown egg is always white the brown dye doesn t penetrate the shell, leaving the inside the original color. There are three breeds that lay :, Araucanas and Cream Legbars. ThePblue color is created by oocyanin, which is applied early in the laying process. PThe blue pigment goes right through the shell, unlike the brown pigment. So blue eggs are blue inside and out. Green egg-layers, such as and, are created by cross breeding a blue-egg-laying breed and a brown-egg-laying breed and those hens possess both blue and brown genes. Therefore the eggshells are green on the outside (created by mixing blue and brown) and blue on the inside, having been painted with both blue and brown dye. Varying shades of browns and greens are for the most part dictated by the breed laying the egg, although within a breed, there might be some shade variation. Some brown-egg-laying breeds apply less brown pigment to the shell than others, resulting in light tan eggs. Some breeds lay extremely light-colored eggs, such as Faverolles and Light Sussex, that can look almost pink or cream in color.


Other breeds, such as Marans and Penendesencas, lay extremely dark brown eggs. Having a colorful egg basketPfilled withPdifferent colored chicken eggsPis just one more benefit to raising your own backyard chickens. Knowing why eggs come in different colors is fascinating. So why not add some color to YOUR egg basket when you choose your breeds this spring? (Of course, when choosing breeds, you should make your final decisions based on temperament, hardiness, and other breed characteristics relating to your climate and location, not purely based on egg color. ) Do you have a favorite chicken egg color? When you purchase chicken eggs at the market, they usually have white or brown shells. But some breeds of chicken produce blue or green eggs. The blue color is caused by, which activates a gene involved in the production of blue eggs. The Araucana, a chicken breed from Chile, andPDongxiang and Lushi chickens in China lay blue eggs. Blue eggshell color is controlled by an autosomal dominant gene:Peggs produced by homozygote chickens are darker blue than those from heterozygotes. The gene causing blue eggshell color is called oocyan (O) and was previously mapped to the short arm of chromosome 1. To further refine the location of the O gene, genetic crosses were performed using molecular markers on chromosome 1. The O gene was then located in a ~120 kb region which contained four genes. Only theP SLCO1B3P was expressed in the uterus ofPDongxiang chickens that produce blue eggs; it was not expressed in chickens that produce brown eggs. Sequence analysis of theP SLCO1B3 revealed that an endogenous avian retrovirus called EAV-HP has inserted just upstream of the gene.


This insertion places a promoter sequence in front of theP SLCO1B3 gene. As a consequence, theP SLCO1B3 gene is transcribed. In chickens that produce brown eggs, no retrovirus is inserted before thePSLCO1B3 gene, and no mRNA encoding the protein is produced. The retrovirus insertion has occurred at different positions in the Chilean and Chinese chicken genomes. This observation indicates that the insertion arose independently during breeding of chicken strains several hundred years ago to produce blue egg layers. The chicken genome contains multiple copies of endogenous retroviruses, which can duplicate and move to other locations. We can assume that a random insertion upstream of the SLCO1B3 gene was selected for by breeding procedures that were aimed at producing blue egg-laying chickens. The SLCO1B3 gene encodes a membrane transporter protein that mediates the uptake of a wide range of organic compounds into the cell. The blue eggshell color isPproduced by deposition of biliverdin on the eggshell as it develops in the uterus. Biliverdin is one component of bile salts, which are transported by SLCO1B3, providing a plausible hypothesis for the role of the protein in making blue eggshells. Blue eggshell color is another example of the important roles that retroviruses have played in animal development. One other is the help provided by retroviruses in producing the. Not all retroviral insertions are beneficial integration next to an oncogene can lead to transformation and oncogenesis.

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