The short-legged form and the Creeper mutation

Japanese Bantam short legs are associated with the Creeper trait, a useful example of how one-copy and two-copy states can have very different consequences. A 2020 primary study identified a deletion on chromosome 7 involving IHH and NHEJ1 in the Japanese Bantam stock examined. One-copy birds showed altered cartilage growth; two-copy embryos did not survive normal development.

The researchers linked reduced IHH activity with delayed cartilage-cell maturation and investigated the consequences of losing NHEJ1 for DNA repair in embryos. These findings explain why the preferred short-legged appearance cannot be considered independently of reproduction. They describe a particular inherited structural variant and its experimental effects, not a universal hatchability percentage for every flock. Sound breed teaching should distinguish genetic expectation, observed embryonic losses and the keeper's actual mating results rather than promise that every egg will produce a short-legged chick.