But way back when, until in the 1880s, Dominiques had either rose OR single combs. Barred rocks owe much of their development to the Dominiques. Even in "pure" Dominique strains, the occasional single comb shows up. While the single combed birds cannot be shown (single combs are a disqualification), they are indications of the recessive gene, and not necessarily from crosses, though that is also a possibility in some lines.