Genetics Question

My short-finned albino bristlenose has spawned with a long-finned normally colored female on three different occasions, about eight weeks apart. All the babies are normally colored with about half having long fins, as expected.

My understanding of genetics and the long-fin trait gets a little muddied after that.

If I were to succeed in spawning two of the long-finned babies together, would it be correct to expect that three quarters of the babies would have long fins, one quarter would be albinos, and three sixteenths would be both  albino and long-finned?
Would it be possible, in future generations, to find a baby with a double dose of the long-fin trait, and obtain a spawn that would be entirely long-finned?

give this a read.

http://www.bristlenoseworld.com/t2500-crosses-interbreeding-bristlenose-updated

in essence you are right but the danger of constantly doing back crosses and sibling crosses is that the inbreeding can result in issues. My advice is that if you are looking for a pure bred individual then look to buy one. Probably be easier, and result in less inbreeding. Personally I dont think that inbred fry should be sold so you will be needing to destroy them.

I have not read anything on if the long fin or any of the color morphs are mendelian traits. But bases on people's experience the long fin trait could be

"""""If I were to succeed in spawning two of the long-finned babies together, would it be correct to expect that three quarters of the babies would have long fins, one quarter would be albinos, and three sixteenths would be both albino and long-finned?""""

----Yes, I got the same thing working out a punnette square, but it is only true if the trait is mendelian and each is controlled by only one gene and if the color morph gene is separate from longfin gene.

""""""""Would it be possible, in future generations, to find a baby with a double dose of the long-fin trait, and obtain a spawn that would be entirely long-finned?""""""

----yes very likely if longfin is an mendelian trait, but you still have to be will selection.