After looking at harlequinboa.com, I think that all we can reliably say is that harlequin is not a single recessive mutant gene. I think the odds are that there is a single mutant gene, but even that hasn't been nailed down beyond doubt. So far, apparently nobody knows whether a snake with a pair of harlequin mutant genes looks different from a snake with a harlequin gene paired with a normal gene.

If most of the boas that have the harlequin mutant do not look normal, but some normal-looking boas can pass the harlequin gene to their offspring, then that could be a case of incomplete penetrance. That sort of thing is known with at least one of the mutants that causes extra fingers and toes in humans. Harlequin seems to be so variable that incomplete penetrance is certainly possible. Proving it would require breeding as many as possible of the normal-looking offspring of a harlequin to normal mating to normal boas. And then figuring out what percentage of those normal-looking boas actually did throw harlequin babies. An interesting but time-consuming problem.

Paul Hollander

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