Just as a small clarification, "null" phenomenon does not bias the clutch to one gender or another. It is acts of parthenogenesis that are typically recognized by one gender morph clutches.
In the link Hooblah posted there is a post by me that has a second link which explains the "null" phenomenon. The "mechanism" is really very simple; a second copy of the gene (in this case the WT copy) is simply missing, by way of any of a number of means.
Except that Russos are quite distinct and not likely to be mistaken for WT animals. And Russo x Phantom looks nothing like a SuperPhantom.
That and the same phenomenon has also been seen with SuperCinny/SuperBlack and it is not like there are cryptic alleles of those out there...









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