While simple recessive involves heterozygous and homozygous expressions, ie genotypes and phenotypes, my understanding of selective breeding is more simple, but almost harder to understand sometimes. Genetics is involved, but more in the matter of blending and indeterminate expression. More like breeding dogs. (CAVEAT -- all dogs are the same species so I am NOT talking about hybrids) If you breed a german shepherd to a lab, the litter will show traits of both parents, but very unlikely any will be a perfect match.
If you then line breed the "lab looking" offspring back to the lab, you'll get more offspring that look more like a lab. Hopefully I haven't gotten this too wrong, or simple.
More particular to the "fine line" boas, I hope Hammond won't mind if I quote what he told me about them:
"The Fine Lines were first produced here in the 1980's from a Colombian male that had narrow saddles and a normal pattern Colombian female. I kept all of the Fine Line offspring back that first year (about a 1/4  of the litter). Five years later these were bred together and with some other unrelated normal pattern Colombians. It is from those litters that they were first put on the market. I have been selectively breeding them ever since. "
Thanks for checking out the picture, and congratulations if you made if through my explanation above!
AndyV

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