What kind of allele results in the trait indicated by the green color being expressed in the individuals shown here?

This is just a dominant allele of the green color trait. The dominance can be confirmed by seeing the commonality of individuals who express the green color trait as having a dominant allele(W) and the ones without(w), not green. This is not X-linked because the letters which dictate the allele do not contain the X character with the a superscript indicating it as a sex-linked trait.

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