I believe this little black chick is the result of Atavism - a potential throwback to the Barred Plymouth Rock male ancestry in the Delaware bloodlines. Atavisms are prompted by the rare reactivation of genes that previously controlled phenotypic features lost many generations ago.
If atavism just means that the person breeding the chickens has produced a chick that doesn't appear to make sense, then yes that fits.
But if atavism is meant to be something that cannot be explained by the usual actions of the usual color genes, then no your chick is not the result of atavism. Your chick is the result of completely normal interactions of several common genes that are acting in the usual, predictable ways.
The following is the genetic basis for that determination.
I think part of your explanation is wrong, and the person at the college didn't help either.
What you said in another thread here was correct:
https://www.backyardchickens.com/th...er-with-white-rock-hens.790644/#post-28467446
Yes, Delawares have barring. They also have the Silver gene, and the Columbian color pattern (with white barring breaking up the black sections into dots.)
Delaware...is not Columbian (another genetic discussion) but a specific arrangement of genes producing white body w/black barring on the hackle, wings, and tail. The barring is due to the B (barring) gene that could be B/B or B/b, where b is the non-barring allele). He only needs the B which is sex-linked and carried on the Z chromosome (males are ZZ, females are ZW). The Delaware male will ALWAYS pass his white-based plumage with black barring to his F1 offspring, both male and female, regardless of the hen crossed.
Correct about the barring, but I'm not sure what you mean by "not Columbian." Do you just mean they are barred + Columbian, or do you mean something else?
Delaware... carries both dominate and recessive white CC/cc and also the silver allele that the Livestock Conservancy was able to isolate and preserve in their recovery efforts.
You seem to have a typo in the abbreviation. Dominant white and recessive white would be II/cc.
You also have an error, because Delawares do not have domiant white, and your rooster does not show recessive white. So he is probably ii/CC, but could possibly be ii/Cc.
Dominant White turns black into white. Delawares do not have Dominant White. Those bits of black in their coloring are the proof of that.
Recessive white turns the whole chicken white. If Delawares were recessive white, they would not have those black dots.
Delawares have the Silver gene. No need to test, no need for special work from the Livestock Conservancy, you can tell by looking at them: that is where all the white in the body comes from. If they didn't have Silver they would have gold, and would have large amounts of gold or red color (like a New Hampshire but with white barring added.)
White Plymouth Rock females are homozygous for recessive white (c/c), which suppresses pigmentation, resulting in solid white plumage.
Yes.
They lack the barring gene (b on their Z chromosome) and do not contribute significant color genes beyond the recessive white.
I can't say if they have barring or not, given that the recessive white hides it all, but you might be right about that.
As for whether White Plymouth Rocks contribute significant color genes: they definitely do if they are bred to a rooster with no recessive white! Once you produce chicks that do not show recessive white, they do show the effect of whatever other genes they inherited from the White Rock, which in this case includes E (Extended Black).
So the little black chick must express significant black pigmentation (E/E or E/e for extended black) and the barring gene (B). His white dot is a hallmark of the B gene, especially in males, as it disrupts pigmentation on the head.
Yup.
My Delaware roo could contribute the B gene (barring) and possibly a recessive e or E allele (from his New Hampshire ancestry) that allows black pigmentation.
Yes on the B (barring), yes he contributes one of the recessive alleles at the e-locus.
However, the White Plymouth Rock female contributes c/c (recessive white), which should suppress color, and lacks the E allele for extended black.
Since recessive white is recessive, and the hen gives only one c gene, then no that will not suppress color in the chick, because the chick inherits C from the father. On the other hand, if the hen has cc (two genes for recessive white), she herself would be white no matter what genes she has at the e-locus.
Given that the chick has E, and the Delaware father does not, it is pretty obvious that the White Plymouth Rock hen does have E.
So for that black chick to appear, his gene writing typewriter would need to somehow bypass the dominant white (I) or recessive white (c) genes that both parents carry, allowing the black pigmentation (E) and barring (B) to express. A rare genetic wrestling match mixing recessives and dominate genes to some how overwrite the genetics of the Roo and Hen, and come out looking like an ancient male ancestor.
Nothing so complicated.
The chick does not have dominant white (I), because the Delaware parent is ii and the White Rock parent is either Ii or ii.
The chick does not show recessive white because it inherited C from the Delaware parent.
The chick inherited E from the White Plymouth Rock parent, and barring (B) from the Delaware parent, and those are what shows in its coloring.
It doesn't take a "rare genetic wresting match," it is a perfectly normal result in that situation.
The TN Ag professor agrees with my hypothesis of atavism and suggested an even rarer possibility could have taken place like a spontaneous mutation or rare recombination event that allowed the black pigmentation (E) to express, bypassing the I (dominant white) or c (recessive white) genes. He said it is less likely but possible in small populations where recessive genes can surface unexpectedly.
No new mutations are needed.
"Bypassing" I (dominant white) is not needed when the chick simply does not inherit that gene.
"Bypassing" c (recessive white) happens any time you breed a chicken with recessive white to a chicken that lacks the gene: chicks have only one recessive white gene, and that has no effect on their coloring.
Without spending $ for genetic testing of the Delaware roo and the Ply White Rock hen, I'll accept the Atavism.
No need for the genetic testing. Just keep producing chicks from that hen and lok at the results. If you breed her to the Delaware rooster, about half of her chicks should be black with white barring. The more you hatch, the more confident you can be that the results are repeatable.
Or if you want to breed that hen to the New Hampshire rooster, at least half of chicks will be black that way too. Sons from that cross might show barring (if the White Plymouth Rock hen has barring too) or might not, but you'll get that answer once you have some chicks that show E (Extended Black.)
My Ply White Rock were obtained from a known hatchery that has been producing this breed for several decades. I buy my rocks from him and they are always consistent. I keep six as my layer flock. All of those hens exhibit the silver allele and I'm confident are purebred dominate white.
If they are pure for recessive white, looking at them will not tell if they have the silver allele or dominant white.
Given that this hen produced the black chick, she could be Ii or she could be ii, but she certainly is not II (pure for dominant white).
Of the two fertilized eggs hatched one appears to be Delaware (I'll have to wait for the first chick molt to validate) and the little black chick.
I can think of several explanations for the white chick.
It might be Delaware colored, which would mean the White Plymouth Rock hen is E/?, with one allele for Extended Black and one allele that allows the chick to show a Delaware-type coloration.
Or it might be white all over.
The white chick might have Ii (dominant white from the mother turning all black into white, none from the Delaware father). That would mean the White Plymouth Rock hen is Ii.
Or the white chick might have cc (recessive white from both parents, which would mean the Delaware father is carrying it even though Delawares usually don't.)
Either dominant white or recessive white would turn the chick white no matter what alleles it has at the e-locus.
I'm growing out their chicks with the White Rangers and in a couple months, I update what these two roosters produced on these 3 hens.
I'm definitely curious to see how the chicks grow up, especially the black one and its full sibling.
And if you breed more chicks from that White Plymouth Rock hen, I'd be especially interested in what colors they are. (And if they show that I'm the one mixed up about the genetics, I definitely need to learn that before I spread it further!)