Shell Brown on Inside Cream on Outside - genetics

[Speilb]

I've never encountered this before. I understood that blue/green was the only color that would be expressed on the inside of the shell. The egg tasted fine by the way.

 

[Ridgerunner]

I’ve never seen an egg quite like that but thanks for sharing the photo. I’ll make a guess at the end of my probably too long post.

We often talk about egg shell color in a very simplistic way. There is one gene pair that sets it up as either base blue or base white. That’s about the only part that is truly simple. The genes that influence final color and shade are pretty complex. At least 13 different ones have been identified and there are undoubtedly many more.

Some of these are dominant or recessive. Some will only act if something else is present. At least one can cause a tinting throughout the egg shell, inside through the outside. I’ve seen that but never one that dark inside.

A lot of those genes just act on the coat the hen puts on outside the egg shell in the last part of the egg’s time in the shell gland. A lot of times in the simplistic version we talk about the blue or white egg going through a paint shop with the color applied to the outside. You can wash that off. A majority of the brown does go on this way, but not all.

Then there is a gene that negates some of the brown that goes on the outside. Even if some brown genes are present if this whitening gene is present you can still get a white egg. From what I’ve seen with my eggs, I think this is probably a recessive gene and it does not counter all brown genes, just some of the browns. The final shade depends on all the brown genes that are present. This last is a guess. I don’t know for sure.

That’s what I think happened with that egg. The gene that causes the tinting throughout the shell was there, something I’ve never seen made that pretty dark inside, and that whitening gene caused the layer that went on the outside to be pretty light. I could be totally wrong.

 

[Speilb]

Thanks for your reply. I guess I posted too soon though. I left the shell out for a while and after a few hours the part exposed to light turned white but remained brown at the edges. The other shell piece that didn't get as much light exposure turned white eventually too but took a lot longer. On both pieces however, the edge stayed brown and still is...

 

[Speilb]