Ok, so spiders are dominant, meaning the gene for spider would be present but does the BEL mask the genes that are present? So the spider gene would be there and genetically it would be a spider but the BEL would not allow it to show?
For example, in basenjis (dogs) the colors brindle and black are each dominant. If the gene for brindle is present the dog will be brindle. So a red dog x with a brindle is going to give you 50/ 50 reds and brindles. A red dog x with a black dog will give you 50/ 50 reds and blacks. But if you breed a brindle to a black, you can get brindles and blacks (and reds if both parent carries red). They will visually be either brindle, black, or red, depending on if either parent has the gene for red. But SOMEtimes, the brindle gene appears on a black dog. You cannot SEE the brindle because brindle is a pattern gene and you can't see the pattern on black. So what really is happening in the litter is this: The brindles are RED dogs with brindle pattern over the top. The blacks are black without brindle OR black WITH brindle. Both genes are dominant so both are expressed. You just cannot see the brindle patterning. Is it possible that the BEL gene is actually masking pattern or color beneath it just as the black does to the brindle?
The black dog with the brindle gene will produce blacks, brindles, and reds (and possibly recessive colors too if they are in there but that is a whole nother ball of wax.)