Most serious breeders use black birds to strengthen their lavender (also known as self blue) breeding program. This is why you will often see eggs from lavender pens described as “chicks will hatch out lavender or black, split to lavender”. This means that in addition to the chicks that hatch out lavender, you may also get some chicks that hatch out black, though that carry the gene for lavender. These are called “splits”. To complicate things even more, depending on how many “splits” are used in a pen, you may get some normal black chicks that DO NOT carry the gene. In this case, they will be described as “chicks will hatch out lavender, black or black split to lavender”. No way to know by looking at them without test breeding if the black chicks carry the lavender gene or not.
Since lavender has become such a popular color, the large hatcheries have been producing large numbers of lavender birds without taking this into consideration, resulting in poorer quality birds that often exhibit the shredded feathers associated with lavender colored birds. Serious breeders use high quality black colored birds to help prevent this.
Here is a visual chart you may have seen other places that may help explain the genetics.
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