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The essentials of the breed: what it is, its genetics, and why it is not a Lizard.
The London Fancy is defined by a unique genetic mutation, progressive greying: a progressive loss of melanin-producing cells after the juvenile plumage. The result is the contrast of a light lipochrome body with dark wings and tail.
They share a historical origin in Spitalfields, but are genetically distinct breeds. Progressive greying is not the mechanism that produces spangling in the Lizard. Crossing with the Lizard destroys the contrast that defines the breed.