A lot of CBS have red genes in them nowadays, but assume you have a black that is double dominant gene and a red, which is double recessive, the only combo that produces red. Then you will get black but carrying the red gene shrimp. If you black already has the red gene in it, then you will 2 black but red carriers and 2 red.
Those are rough, the thing people forget about genetics and probability and things like that, is that they average out over time. Yes, over time, a coin toss will go 50/50, but maybe the first 100 coin tosses are all heads. If you sample size is 100, it's 100/0, but maybe over 200 or 500 or 60000000000000000 flips, it will be 50/50.
Same with genetics, you may get all black for a few generations, then some reds. The problem with putting CBS into a CRS tank for too long is that because the black gene is dominant, you only need 1 black gene to make a shrimp black, so eventually you may end up with more blacks than red. Again, that is providing the 50/50 thing above, which may happen in 2 generations in your tank, or 90 generations that the blacks take over.
As for the grading, a higher grade shrimp can throw out any lower grades, and sometimes lower grades will good genes (like a S grade that came from an SSS+), that S grade could throw out some SS or maybe even SSS grades.
Generally, they don't jump up or down grades too often, but that is why there is culling, because it does happen. It's the way we got the higher grades. Lower grades popping out higher ones and they were removed and bred and now we all kinds of grades, patterns, etc. Since all crystal shrimp came from what we call C grades in the beginning, any shrimp has the gene's, and therefore, potential to throw out lower grades.
20g platy, , 2 x 10g shrimp, 3 x 20g shrimp, 7.5g shrimp and 1 great dane/mastiff puppy.
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