10/15/2025
Excellent explanation of the genetics of black!
🧬 It's Genetics Tuesday!
Let’s talk about one of the most dominant and misunderstood color genes in poultry: Extended Black, located at the MC1R locus (the Melanocortin-1 Receptor).
This gene doesn’t just decide color; it controls how pigment cells behave at their core. Normally, MC1R acts like a light switch. When it’s off, pigment cells make pheomelanin (the reds, golds, and tans). When it’s on, they make eumelanin (the blacks and browns). But when a bird carries the Extended Black (E) allele, that switch gets jammed into the “on” position permanently. The result is nonstop eumelanin production from head to tail, creating a solid black bird and completely masking most of the pattern genes underneath.
That’s why you can breed colorful parents and end up with a pen full of black chicks. Extended Black doesn’t create pigment, it controls it.
This gene sits at the top of the E-locus hierarchy, above birchen (Eᵇ), wild-type (e⁺), and wheaten (eʷh). Because E is fully dominant, even one copy can override everything it’s paired with. A bird that’s E/E or E/e⁺ will appear black-based no matter what other color genetics it carries.
Extended Black doesn’t always act alone, though. It interacts with dilution and modifier genes that change how that black pigment looks.
Add the blue (Bl/bl⁺) gene and the bird turns slate blue or splash.
Combine it with lavender (lav/lav) and it fades to a soft lilac-grey.
Pair it with chocolate, either recessive or sex-linked, and it transforms into a warm brown.
Even recessive white (c/c) can completely cover the black, producing a white bird instead.
Some modifier genes like Mh (Mahogany) or Db (Dark Brown) can also cause brassiness or leakage by re-activating small areas of pheomelanin. That’s why black roosters sometimes show copper or red tones in their hackles, the underlying color is still there, just fighting through the dominance of E.
At a molecular level, the extended black mutation is a gain-of-function change in the MC1R gene. It alters the structure of the receptor so it remains active all the time, even without the normal hormonal signal that should trigger pigment production.
Different breeds may have slightly different versions of this mutation, which explains why some “black” lines are darker and more saturated while others show faint leakage or softer charcoal tones.
For breeders, understanding extended black is critical because it can hide a flock’s color genetics for generations. You might have birds that appear jet black but actually carry hidden genes for partridge, duckwing, or even wheaten. Once those birds are bred to a mate that doesn’t carry E, those hidden colors can suddenly resurface in their offspring and that’s usually when breeders start scratching their heads wondering what just happened.
Extended black doesn’t erase color; it hides it. It’s the foundation for some of the most striking varieties we see today. Those deep blacks, blues, splashes, and chocolates, but it’s also the reason “mystery chicks” show up in hatches that were supposed to be predictable.
The next time your hatch turns up darker than expected, don’t panic. That’s not random, it’s MC1R flexing its dominance once again.
