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I have been researching the question. Todays standard for the American dominique has a rose combs. Some flocks carry the allele for strait (tall single) comb at a low frequency. The single comb is recessive so in flocks where allele is rare, birds within same flock that homozygous and thus exhibit the trait are even more rare.
Some folks do not distinguish between American dominiques and barred plymouth rocks, the latter has a straight comb, even though the two breeds differ noticeably for several other characters.
One of the hatcheries I acquired dominique chicks from had about 10% strait combs and a characteristic of feather development that makes me think they have a considerable amount of barred plymouth rock. What you are looking at may be of similar origin.