Blue Egg Gene Guide
The Blue Egg Gene Explained
What makes an egg blue, how copies are inherited, and what a test tells you before you pair birds.
Blue eggs come from a single dominant gene, usually written O for oocyan. It causes biliverdin to be deposited through the whole thickness of the shell, which is why a blue egg is blue inside as well as outside. Brown pigment, by contrast, is painted on at the end, which is why you can scrub some of it off.
🥚 Blue plus brown makes green
That layering explains almost every question we get. A hen with the blue gene laying over brown pigment produces green, which is what an Olive Egger is. No separate green gene exists. Depth of green depends on how much brown pigment sits on top, and that is a separate set of genes entirely.
🧬 Copies and what they mean
| Result | That bird lays | What it passes on |
| 0 copies | Brown or white eggs | Nothing. It cannot produce blue laying daughters with a non blue mate |
| 1 copy | Blue or green eggs | Blue to roughly half its chicks |
| 2 copies | Blue or green eggs | Blue to every chick |
Because the gene is dominant, one copy and two copies look identical in the egg basket. That is the whole reason to test. A one copy hen and a two copy hen lay the same blue egg, but only one of them guarantees blue laying offspring.
👀 Why you cannot tell by looking
- Roosters lay no eggs. A cockerel can carry one or two copies of the blue gene with nothing to show for it, and he is half of every pairing you make.
- One copy and two copies look the same. Shell color cannot separate them.
- Easter Eggers are unpredictable. They are a mixed background, so a hen sold as an Easter Egger may carry one copy, two, or none.
- Pullets have not laid yet. Testing a young bird answers the question months before her first egg.
✉ How to test
Send a freshly plucked feather with the soft base attached, or a blood spot on plain paper for a bird too young to have usable feathers. The same sample can be used to sex the bird at the same time, which is what most people do with a hatch of Ameraucana, Cream Legbar, or Olive Egger chicks.
Turnaround is 2 to 3 business days from the day your samples arrive at the lab. There is no collection kit to buy or wait for. Bundles of 8, 25, 50, and 100 samples bring the per-bird cost down when you are testing a whole hatch.