Sex-linked barring Part 1!
This is the gene that is responsible for black sexlinks. It is sexlinked incomplete dominant.
b+ is the non-barring allele
B is the barring allele
Barring interrupts pigment production, creating bars of almost no pigment and bars of almost saturated pigment. Barring shows up best on a black base. This will allow for almost black and almost white bars. Other colors show good barring as well, but in some, it is very indistinct. Wheaten barred hen feathers and the blue barred feathers have especially blurry barring.
Because barring is on the sex chromosome, females can only inherit one barring allele. This would make them hemizygous for barring.
B/-: cuckoo d'Anvers female named Margaret
Here is a male with only one copy of barring. Since he had no selection in his background, he has some solid black feathers (however, even the best barred birds can have black feathers, they simply remove them for show). As you can see, he is roughly the same color as the hen above.
B/b+: Single barred d'Anvers male (His name was Stripes!)
With two copies of the barring gene, males will have more white bars, giving them a much lighter appearance.
B/B: double barred DominiquexD'Anvers cross (cage bars not always included)
Some of you might point out that all of the birds I just posted were cuckoo, not barred. It is true that barring as defined by the Standard of Perfection has much cleaner and more even bars while cuckoo is more rough around the edges.
An exhibition barred Plymouth Rock would be barred while a hatchery "barred Rock" would actually be cuckoo.
Why is this? The slow feathering gene, and also selection for better barring.
The "slow-feathering gene" is a sex-linked mutation that causes a bird to feather in more slowly.
Exhibition barred Plymouth Rocks have the slow feathering gene. I should know. I had one and his feathers came in slooowly. (Sadly, I lost whatever pictures I had of him.) This allows the bars to come in evenly.
Hatchery "Barred Rocks", Dominiques, d'Anvers, and most other breeds have the fast feathering gene. So their bars look like a rush job. I'll explain slow and fast feathering at a later date.
However, "barred" and "cuckoo" from a genetics standpoint are both barred. For simplicity's sake, I'm going to call them both barred.
Anyway, a neat thing about sex-linked barring is that if you have a true-breeding flock of B/- females and B/B males, you can sex them based on color.
All the dark chicks with white spots on their heads are barred. Large, irregular white spots indicate male chicks. Small, even white spots indicate female chicks. And once their feathers come in, the difference between homozygous double-barred males and hemizygous single-barred females is even more obvious. However, there is a lot of variation in barring. Some lines are lighter and some lines are darker. Since these barred chicks have a mixed heritage, even though they are homozygous and hemizygous, all of the chicks look very different and I probably couldn't reliably sex them.
On certain base colors, barring can be used to create autosexing chicks, a topic that definitely deserves a post of its own.
I also never got to sex-link crosses. I will have to make a part 2, maybe even a part 3!
