Easter Eggers: Understanding Egg Color Genetics

Unusual colored eggs have become quite popular among backyard chicken keepers. There have been many a debate about the differences between pure blue-egg-laying breeds and the much more common Easter Egger chicken. Pure breeds such as the Ameraucana or Araucana have a specific Standard of Perfection (SOP) that is accepted by the American Poultry Assoc (APA) &/or American Bantam Assoc (ABA). The SOP is a very specific list of defined variations within the breed that must not only be present in the bird but also breed true (show consistently in the subsequent offspring) in order to consider the bird to be a pure breed. On the other hand, Easter Egger (EE) chickens are not a breed at all; they are actually a hybrid or crossbred offspring from a bird that carries a blue egg gene. All of this aside, the steps for creating an EE that lays green/blue eggs are not overly complicated. Below is a condensed explanation of breeding EasterEggers.
[Note: this is intended to be a quick guide & does not cover all details of genetics]

Genetic basics:

  • Every genetic trait is produced from a pair of genes, and in reproduction each offspring receives one gene from each parent to create a pair for its genetic traits.
  • If a chicken is homozygous, it carries the same two genes for a specific trait; heterozygous means it carries two different genes for a specific trait.
  • Some genes are dominant, meaning the dominant gene will mask any other genes present (recessive).
  • There are also other factors like alleles, modifiers and inhibitors that affect the genes for specific traits.
  • There are only two genetically determined egg colors: white and blue. The blue egg gene is dominant.
  • Brown eggs are produced by an allele that produces a brown coating over a white egg. Thus, green eggs come from a brown coating over a blue egg.
  • The allele for brown eggs is dominant, meaning if it is passed to offspring it will mask other genes, alleles, and modifiers.

Pure Ameraucana (and some other breeds) are homozygous for blue eggs (O/O). This means that all offspring from a pure Ameraucana will receive at least one blue egg gene, and since that is a dominant gene, the eggs produced will be blue.

Regular brown egg layers are homozygous for white eggs (o/o) and carry the brown shell-coating allele. [designated here by o/o]

Crossing chickens carrying the above genes results in the following possibilities:

F1 EE

O/o = a genetically blue egg because the O is dominant
But, don’t forget to add the dominant allele for the brown eggshell coating, now you have a green egg!

Now, what happens if you breed a 1st generation* (F1) EE to another brown egg layer?

*Must be a first generation (F1) EE to ensure it carries the O/o genetics!!

Crossing an F1 EE (green egg layer) with a brown egg layer results in the following possibilities:

F2 EE

And what happens if you breed two 1st generation* EE’s to each other?

*Again, this must be first generation EE to ensure they both carry O/o genetics!!

Crossing an F1 EE to an F1 EE results in the following possibilities:

EEtoEE

Don’t forget to add in the dominant brown eggshell allele, and most of the eggs will result in shades of green or some will be brown. However, occasionally the brown eggshell allele will not be passed (or will be effected by an inhibitor, modifier, or other allele), and the results will be a nice blue egg or less commonly a white egg.

As you can see, past the first generation (F1) breeding, the genetic combination possibilities increase and become more difficult to determine exactly what genes are involved, especially in roosters that do not lay eggs. Additionally, using a non-pure breed (chickens of which you do not know the exact genetic make-up) can introduce recessive genes or genetic inhibitors that might not be obvious on the parent, but will affect the outcome of the offspring.

Note: White egg layer genes, while not dominant, typically act as an inhibitor to dilute any other egg color genes. We bred a 1st generation OliveEgger to a Leghorn, and the result was a pale olive colored egg layer.

Additionally, it should be noted that many EE’s are difficult to differentiate from a pure Ameraucana breed. Since the muff/beard genes are dominant, many EE’s will carry these genes. The gene for the pea comb is located very near the blue egg gene, and is often passed with the blue egg gene. However, while pea combs often indicate the presence of the blue egg gene, it is not guaranteed, and it also does not indicate homozygous or heterozygous genetics. For a reason that we have not studied, EE’s very often have green legs which is a good indicator of non-pure-breed genetics as the pure blue-egg breeds do not have green legs. It is extremely important to know the genetics of the parent birds in order to use the information provided here. If not starting with pure genetics, then the bird could carry any number of genetic factors that will change the outcomes – even pure birds can occasionally have some genetic faults that pop-up unexpectedly.

For your reference:
Unscrambling the genetics of the chicken’s ‘blue’ egg: Researchers have unscrambled the genetic mutation that gives the distinctive blue eggs laid by some breeds of chickens.

Find A Blue Chicken Egg? Congrats, Your Chicken Has A Virus: A new study found that a single gene, called callee oocyan, is responsible for the odd coloration of these blue chicken eggs.

Genetics Mini Series 1: Genetics of Egg Color

Genetics Mini Series 2: Breeding for Blue Eggs

Genetics Mini Series 3: Breeding For Other Egg Colors

ALL ABOUT EGG COLOR: Have you ever wondered what makes blue eggs blue or why a green egg layer might hatch from a blue or brown egg? Did you know that brown eggs are coated with a “paint” made from blood, and blue egg shells contain a chemical byproduct of bile? Read on to find out the science behind egg color.

 

One Comment on “Easter Eggers: Understanding Egg Color Genetics

  1. Pingback: Olive Eggers: Breeding for Olive Eggs – Mo's Mini Farm

Leave a Reply

%d bloggers like this: