Sorry to rain on your parade. At least it's not a frustrating mystery anymore. Now at least you know the formula. I've found not many on this forum have taken the time to understand chicken genetics, so you are not alone. It seems daunting, so few attempt it. It's really not that bad.
Everything I learned beyond highschool genetics I learned online.
It's the terminology that's confusing, but the mechanisms are relatively simple. They work well for those who think in concrete terms and like formulas.
I was not a math major, and preferred Geometry to Calculus. I liked what you could see and measure with your eyes. Genetics is fairly concrete.
I think it helps to know that chickens, like humans, carry genes in pairs, one from mom and one from dad.
EXCEPT the genes that are sex-linked. These are genes like Gold/Silver, Barring, Pale/Dark shanks and the Fast/Slow feathering.
Of those genes, the hen only has one rather than a pair, and she gets it from dad. Every time, no matter what. Roosters carry these in pairs, like all the other genes, one from mom and one from dad.
For all genes, they are kind of like two sides of a coin. They determine feathered shanks or clean shanks, peacomb or straight, etc. That is why you hear about traits being either recessive or dominant. In people, blue eyes are recessive, brown are dominant. In chickens, peacomb is dominant, straight comb is recessive. It is the same with all the genes used for determining gender. The sex-linked genes.
For example, Silver is dominant to gold(white base color vs. tan base color), Barred over non-barred, Pale shanks over dark, and Slow over fast feathering. Dominant means that when paired, if there is one dominant and one recessive form of that gene, then the dominant trait is exhibited. Recessive means the opposite: that it ONLY exhibits if there are a pair of recessives, and does not exhibit when paired with a dominant form.
That's why the HEN has to have the dominant form of the gene and dad has to have a pair of the recessive form.
The hen passes that dominant form to her sons, who get the recessive form from dad. The dominant prevails over the recessive and they exhibit the trait (barring, slow feathers). The girls only get the one recessive gene from dad, and do not exhibit the trait (no barring, fast feathers)
If it were reversed, and dad had the dominant form, say slow feathering, and mom carried fast: Dad (because he has a pair of these dominant slow genes) passes slow on to both his sons and daughters. Mom only contributes one recessive gene to her sons, and they end up with one from mom and one from dad. Because what they get from dad was the dominant form, it doesn't matter what they get from mom, they still exhibit what they get from dad, just like all of dad's daughters... = can't determine the sex because all the offspring were given the dominant form from dad. If dad is heterozygous for a trait (carries one dominant and one recessive form) he passes either of these forms randomly down to all of his offspring.
I think all of the sex-linked genes are considered to be incompletely dominant. That means if a rooster has one Silver gene and one gold gene, then his background color is not white or tan, but something in between. He needs two silver genes to exhibit the trait perfectly. Since hens only get one gene, they are only either, silver or gold.
Barring works the same way. That is why barred hens are darker than purebred barred roosters. They only get one barring gene, and roosters get two- they call this a double dose, so their barring is more extensive and results in more numerous narrower bars.
This is also why our BCM hens have darker shanks than the roosters. Our roosters get a double dose of the Id gene that lightens shanks. Hens only get one.
There are still lots of things related to chicken genetics that are being discovered and determined. It's not all nice neat theory either. But most of the basics are fairly simple.
So you see it's not all lab-geek mumbo jumbo. Or is it??? Maybe I am a lab-geek.
Did it help?
Pink: I hear you... I think there are definitely gender determined differences in feathering rates, they are just subtle and not consistent. I have two wheaten girls who are on opposite ends of the spectrum in feathering, and I knew their genders on day 3 because of the color. I think the general rule is girls feather out faster, but on my UK BCM the boys grew huge primaries overnight and left the girls in the dust. I think when it's the day-old little primary pin feathers, the genetic theory above holds fairly true. When you're looking at tail feathers, dorsal line feathers etc. at 10-14 days it's definitely not just influenced by slow/fast feathering, but also by gender. Maybe your whole flock is homozygous for either fast or slow, and it doesn't mess up the gender related rate difference.
I think your eye is also trained to notice subtle differences in beak, comb, leg etc. and your mind puts all the data in with the subtle differences in feathering to give you your final verdict.
Honestly I stopped fretting over it, because I would never cull a chick based on gender, so I just wait. I wouldn't treat them any differently if I knew their gender at 2 days or 2 weeks or 2 months, so I just have fun watching them grow, and watch things like growth rates, feather coloring, etc. to help me determine who I keep.
