Breeding EEs - gene questions

[Ridgerunner]

Tim, thank you. I learned something. For those that don't know, Tim is one of the true chicken genetics experts on this forum.

If you don't mind, could you expand a bit on why I got the results I did. The mothers were red EE's of unknown background, probably different hens for each chick, though there could be some duplication in mothers. Fathers were either a welsummer of another red single combed rooster, possibly a RIR if my memory is right. All five eggs were green.

I got one pea combed rooster and four pea combed pullets. Out of the four pullets, one laid green eggs and the other three laid brown eggs, pretty much pink. From your post, I would have expected each pullet had a 97% chance of laying green eggs since all the chicks had a pea comb, yet only 25% did. I realize this was a small sample so the percentages don't mean a whole lot, but was I just unlucky or is there possibly something else working too?

I'd appreciate any help you could give on my understanding this.

Thanks.

 

[tadkerson]

Did you get a true pea comb in the offspring or was it a modified single comb?

It has been my experience that the pea comb is incompletely dominant to the single comb. In my birds, if I crossed a purebred pea combed bird with a single combed bird; the offspring had a weird looking modified single comb. The male combs had a single blade but at the top it had rows of small spikes. The female comb was also unusual- like a wide noodle that flopped to one side.

You would get the results you stated if the hens only carried one blue egg shell gene. The hens would have on chromosome # 1 a blue egg shell allele and a pea comb gene. One the other chromosome # 1 they would have a white shell allele and a pea comb gene. This ( pea comb linked to white egg shell) can occur if crossing over occurs during meiosis; it happens about 3% of the time in birds that are hybrids. It does not occur in birds that are purebred.

So your hens would be O/o+ and P/P. If you crossed your hens with males that carry o+/o+ (brown egg layers) , normally one half of the offspring should inherit the blue egg shell allele. If you hatched out 20 or more eggs, the numbers should approach 50% inheriting the blue egg shell allele. Your numbers are small ( as you stated) so the results are skewed.

I hope I explained the results- if you have more questions please post.



Tim

 

[Ridgerunner]

I only have the one green egg layer left. I'll try to look at her comb closer tonight on the roost. The others did not meet my requirements for the breeding flock. I don't remember their combs being anything but pea, but I'll admit I did not look real close. I just knew they were not single. Again, I have learned something. That incomplete dominance stuff in chickens is going to drive me nuts.

I think what you are saying is that the parent EE hens probably had one pea comb gene associated with the blue egg gene and one pea comb gene not associated with the blue egg gene. A 1 in 4 split is pretty normal for a 50-50 chance.

4 out of 4 on the pea comb is also not that unusual on a 50-50 chance, but with that blue egg gene 97% tied to the pea comb, I was really confused. Even my luck usually doesn't run that bad. Thanks. I think I understand it better.

 

[tadkerson]

Quote:
Your probabilities of inheritance are correct if the cross deals with a typical single locus with two alleles. The problem is that the green and brown color in eggs is polygenic so the percentages do not apply.

Blue X green= green

green x green = green


Tim

 

[Ridgerunner]

Quote:
Here you go confusing me again. I though the basic blue or white color to the shell was a single locus with two alleles. It is either blue or white. With a green egg, you don't know if both alleles are blue or if they are split for blue and white, so that will definiitely mess with the percentages.

I thought the polygenic factor determines the shade of white, blue, brown or green?

Say you cross a white egg laying leghorn with a blue egg laying EE. The EE may be split for blue-white base shell color or pure blue-blue. So you would either get 50-50 blue/white egg layers or 100% blue egg layers from this cross, depending on whether the blue egg layer was split or pure for blue.

Then if both green egg layers (realizing the rooster does not lay eggs) are split, you would probaly get a 3 to 1 ratio of green to brown egg layers? If one is pure for blue, they are all green?

 

[tadkerson]

The green color and brown color are polygenic because green eggs are blue (one gene) and brown (polygenic). Brown eggs are polygenic.

Blue eggs are O/o+ or O/O.

Green eggs are O/o+ or O/O plus a number of genes for brown egg shell


Blue X Green

could be ratio of 3 green to 1 brown or 100% green; the three to one ratio is due to a hybrid cross Oo+ x Oo+ , the chicks that inherit white egg color(o+/o+) will also inherit some genes for brown egg color and produce the brown eggs.


Green X Green

could be ratio of 3 green to 1 brown or 100% green; the three to one ratio is due to a hybrid cross Oo+ x Oo+ , the chicks that inherit white egg color (o+/o+) will also inherit some genes for brown egg color and produce the brown eggs.



Blue X Brown

Could be 1 green to 1 brown or 100% green, the one to one ratio is due to a Oo+ x o+o+ cross , the chicks that inherit white egg color (o+/o+) will also inherit some genes for brown egg color and produce the brown eggs.



Blue X Blue

In this case, the inheritance deals with only one locus and two alleles. This cross would follow simple Mendelian genetics.

100% blue or 1 blue to 1 white or 3 blue to 1 white



Tim