Expected percentage of Yellow Bellies from YB (YB/wt) x Normal cross?

50%

Since the Yellow Belly trait is co-dominant, a snake visually identified as a Yellow Belly carries one copy of the gene, represented genetically as YB/wt (heterozygous). When this snake is bred to a normal wild-type snake (wt/wt), each parent contributes one allele randomly. The theoretical expectation based on Mendelian principles is a 50% chance of the offspring inheriting the YB allele (resulting in a visible Yellow Belly) and a 50% chance of inheriting only the wild-type allele (resulting in a normal offspring). This predictable 1:1 ratio is a standard outcome when breeding a heterozygous co-dominant animal with a baseline wild type.