True or False? Olive egg genetics.

[nicalandia]

The best information I have says the oocyanin gene is located about 80 centimorgans up from the allele that controls pea comb/straight comb. From work I've done with plants, a crossover occurs about 3 times per 1000 when the genetic distance is 80 centimorgans. I can't say that this is applicable to chickens, but it is a good starting point. If you read up on the history of the Whiting Blues, he was able to find a crossover and develop a straight comb version. I don't think the straight comb birds have been released.

One of my goals with the DNA tests is to nail down the pea comb allele location on chromosome 1. It is a separate project from the blue egg tests. Said another way, we could use a good test that could differentiate straight comb from pea comb on chromosome 1 and could ID the rose comb inversion on chromosome 7. It should be relatively simple to set up a DNA chip to detect rose comb, pea comb, straight comb, and blue egg.

One of the aspects of pea comb that causes problems is that it is dominant over straight comb. You can still usually tell that a bird is homozygous pea comb by the size and structure of the comb. Given the low crossover rate, always breeding from pea comb birds is one way to select for blue egg layers. Unfortunately, if you want rose comb - as i do - you have to breed away from pea comb. This is because combining the rose comb inversion with pea comb results in a walnut comb, not a rose comb.

There is a third allele of the same gene that controls straight and pea comb. It causes an inverted tip on the comb looking somewhat like a short walnut comb. I have not looked up cushion comb to see if it also is an allele. This is just speculation on my part, but given the location on chromosome 1, there is a very high probability of several more mutations affecting the straight comb gene.

its about 4 cM(centi Morgan or m.u map unit) its about 1% chance of recombination per cM, so about 96% chance of getting a blue/egger if one starts with a Pea Comb breed like Araucana or Ameraucana.
https://reader.elsevier.com/reader/...egion=us-east-1&originCreation=20210427001714

Once the linkage is broken, the recombinant is linked to the single comb p+ allele(P an p+ are allelic).

Breeds like the Cream Legbar and Isbars can trace their lineage to Dr. Punnett line of chilean stock, they were single comb.

Also, Pea Comb has already been maped to Chromosome 1 on the chicken genome, its been given the name SOX5

 

[Allsfairinloveandbugs]

This thread is extremely informative. Actually, the OP had their question quickly answered, & hasnt been seen since. I am the one who started asking further questions!

@DarJones, your zinc white gene input is fascinating. Even more so, that the zinc white gene causes eggs to appear light tan, even if the zinc white covers a blue egg! Im going to crack some light tan eggs from white leghorn and blue andalusian progeny, & check if the inner shell is blue. I had always assumed an easter egger roo with one brown egg gene caused the light tan eggs. Maybe not!

Im currently not sure my blue andalusians carry the zinc white gene. The white leghorn eggs are a beautiful bright white (and jumbo-sized). The blue andalusian eggs appear much duller. (And are much smaller). The white leghorn eggs look as though they are painted with high gloss paint, & the blue andalusians with flat white. Was frankly disappointed in the blue andalusian eggs. Only purchased andalusians once, 4 years ago.

I had previously read the pea comb gene (from an ameraucana or aracauna) is approx. 96% linked to the blue egg gene. Due to a ridiculous number of broody hens over the years, my easter egger hatch rate has Not been small. Have hatched enough over the years to see a handful of hens with pea combs lay brown eggs, & also a few hens with straight combs lay green. (Cant remember if any straight-combed hens laid blue). I keep the straight-comb layers and pea-comb layers separate for breeding/ hatching purposes, so egg color anomalies stand out. One oddity that also stood out was a straight-combed pullet that laid blue eggs with brown speckles. No green color in egg at all. She was a very poor layer; only laid 1-2 eggs weekly her first year. The poor lay rate stood out too, since my flocks have otherwise had excellent lay rates (approx. 6 eggs weekly during first year).

I had no idea a dna test can determine if a roo is homozygous for blue egg genes. I had read a small, tight pea comb (as opposed to a larger, floppy non-conforming pea comb) can help identify a homozygous easter egger roo. But since i definitely want to keep homozygous blue egg genes in my flock members, a dna test on a few chosen roos is a great avenue to consider.

Thanks again for everyone's input. There is a wealth of information here, going far beyond the original question about olive egg genetics. And the additional info is still relevant, since it takes blue and (dark) brown to make an olive egg!

 

[DarJones]

that the zinc white gene causes eggs to appear light tan, even if the zinc white covers a blue egg!

Sorry, this came out just a tad different than reality. If a chicken with the zinc white trait is crossed to a brown egg layer, the eggs appear light tan, especially if first wiped with water. If a blue egg layer with the zinc white gene is crossed to a brown egg layer, the eggs appear light tan over pale blue. A single copy of the oocyanin gene produces slightly paler blue eggs than being homozygous for the oocyanin gene. The emphasis is that the presence of the zinc white egg trait almost completely blocks the porphyrin biopath that produces a brown coating. It does not in any way impede the oocyanin gene other than the difference between hemizygous (1 gene) and homozygous (2 genes).

I'm still trying to document the 4 centimorgan distance nicalandia posted. So far, I've found a 2018 research article that states the oocyanin mutation is "adjacent" to P (pea comb). This suggests a far lower rate of of crossover than the 4% stated. It is still possible given that there are some segments of DNA that are highly active in crossovers. If an active region is between oocyanin and P, the result could easily support the 4% rate. It is interesting that there are currently 4 breeds with straight comb that lay blue eggs. Anecdotally, I've been told of a few fanciers who had single comb blue egg layers show up after a cross with Ameraucana's.

 

[Allsfairinloveandbugs]

water. If a blue egg layer with the zinc white gene is crossed to a brown egg layer, the eggs appear light tan over pale blue

I try to absorb carefully before i reply. So, in the above cross, the resulting phenotype is light tan. Period. Not green (brown over blue), or light brown (brown over white), as would normally be expected when crossing Blue/White x Brown/Brown. Did i get that right?

 

[DarJones]

Dead on the money. There were zero green/olive egg layers in my F1 crosses with blue egg laying leghorns. All of them lay tan over pale blue eggs due to the presence of the zinc white gene(s). It is likely that some olive eggs would show up in F2, F3, etc given the level of segregation. Constant selection for blue eggs has kept this from occurring in my chickens.

 

[NatJ]

I'm still trying to document the 4 centimorgan distance nicalandia posted. So far, I've found a 2018 research article that states the oocyanin mutation is "adjacent" to P (pea comb). This suggests a far lower rate of of crossover than the 4% stated. It is still possible given that there are some segments of DNA that are highly active in crossovers. If an active region is between oocyanin and P, the result could easily support the 4% rate. It is interesting that there are currently 4 breeds with straight comb that lay blue eggs. Anecdotally, I've been told of a few fanciers who had single comb blue egg layers show up after a cross with Ameraucana's.

You could try "Genetics of the Fowl," a book by F. B. Hutt, published in 1949.

I found it for free, on Cornell University's website, but I can't figure out how to make a link that works. (I just googled for the title & author.)

Chapter 14 talks about linkages between genes, and mentions "O (blue eggshell), which Bruckner and Hutt (1939) found to show only about 5 per cent of crossing over with P."

 

[Allsfairinloveandbugs]

Dead on the money. There were zero green/olive egg layers in my F1 crosses with blue egg laying leghorns. All of them lay tan over pale blue eggs due to the presence of the zinc white gene(s). It is likely that some olive eggs would show up in F2, F3, etc given the level of segregation. Constant selection for blue eggs has kept this from occurring in my chickens.

Fascinating!

 

[DarJones]

Bruckner and Hutt (1939) found to show only about 5 per cent of crossing over with P.

That is where I have a problem. If P is adjacent to O as suggested by a 4 centimorgan distance, there should be a LOT less crossing over than 5%. 4 centimorgans would be more in line with .01% crossing over which is 2 orders of magnitude less. Please note that I am not saying this is incorrect. I am saying that from a genetic perspective, I would expect a lot less crossing over for adjacent genes. There are some reasons this can occur including having a highly active genetic region between the two genes. The more probable reason is that the actual mutation for oocyanin is on an arm branch of the chromosome and the arm branch provides an extended area for translocations to occur. I'm certain this can be resolved from existing documentation. We will see.

 

[VeryHappyHens]

Some other chicken keepers told me something interesting. I wasn’t sure if it was true or just something they had been told, but...
Anyways, this is the basis of it:
When you cross a blue layer with a brown layer, you get green eggs. And if you breed a f1 hen and a rooster of this cross, you can‘t get more green eggs. They are only blue or brown.
They also muttered something about “true olive eggers” being different.
I was skeptical, but I thought I would ask you all.
Thoughts?

False. Specifically because the offspring has 75% green egg gene 25% brown egg gene.

 

[NatJ]

That is where I have a problem. If P is adjacent to O as suggested by a 4 centimorgan distance, there should be a LOT less crossing over than 5%. 4 centimorgans would be more in line with .01% crossing over which is 2 orders of magnitude less.

But when I look up "centimorgan," it is a measurement of the rate of crossover.
1 centimorgan = 1% chance of crossing over.
So 4 centimorgans = 4% crossing over.
And 5% crossing over would be 5 centimorgans.

Are you working with a different definition of centimorgan?