The only way to tell is to breed them to prove them out. I bought a super lesser pos GHI, pastel, and/or spider from garrick demeyer. Im guessing if there was a way to tell then he would know so he could charge an accurate price for the snake. However, he just said she is possibly those other 3 genes. Spider is one that is said to show a pattern under a black light. Does that mean if a BEL has the spider gene itll 100% of the time show a pattern under a black light? No one knows. Unless you spent years and years just breeding and experimenting with BELs maybe?