One of the things that makes subocs unique is their unusual chromosome number-40 compared to 36-38 for other native colubrids. Since chromosomal pairs won't match up, all the eggs from these crosses would be infertile or incapable of normal development.
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Brad Chambers
WWW.HCU-TX.ORG

"Some things are flat impossible-until they're done."
Robert A. Heinlein