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double factor- A genetic term that means a bird is carrying a mutation on both chromosomes of the pair. Term usually restricted to a trait that is not completely dominant so that a single factor shows the trait in a modified form. For example, a double factor for yellow body color in a male Gouldian finch has a yellow body while the single factor is just a dilute normal. Of course there are always exceptions and the white-chested single factor male looks like it is a double factor yellow.