Description:
The Rose Comb gene is one of the first genes to ever be classified in chickens, and was noted to be autosomal dominant (2). It actually was proposed by Punnett and Bateson and used to prove classical Mendelian genetics in everyday animals (think punnett squares). (2)
Rose Comb causes the normal single comb to flatten out and widen through the head. It has a low, rounded profile unlike the pea comb gene, and has a distinct spike, called a leader, that comes from the back of the comb and either lays flat on the head or extends a bit upwards. (3) It is typically bumpy in texture, though there is a possible separate smoothing gene that causes the comb to be smooth and flat across the top. Typically this smooth look is desired (3).
Originally, the rose comb in homozygous form was thought to cause fertility issues, noted in Wyandottes especially (4)(5), however it was later found that there were actually two different versions of the gene at different alleles--one at R1 and another at R2. Only the R1 type rosecomb caused fertility issues, while the strains with R1 rosecombs did not (6). It is unknown how common the R1 strain is compared to R2 in breeder flocks.
APA and ABA accepted breeds with the natural rose comb include the Ancona, d'Anver, Dominique, Dorking, Hamburg, Leghorn, Minorca, Nankin, Redcap, RIR and RIW, Rosecomb breed, Sebright, and Wyandotte (3).
The rose comb also works with the pea comb gene to create walnut, strawberry, and cushion combs. The walnut comb is a broad, circular comb in the middle of the head, with slight ridges all the way through. It is often created with the rose comb gene with a copy of the pea comb gene. (5). The cushion comb is thought to be the walnut comb plus the smoothing gene, though more information is needed about this gene as it hasn't been studied in common literature. The strawberry comb is believed to be just a selected walnut comb, though more information is needed.
The only accepted breed with the walnut comb is the silkie (3).
The Chantecler is the only breed accepted with a cushion comb (3).
The Malay is the only accepted breed with the strawberry comb (3).
Rose Comb is a dominant gene. It is worth noting that the heterozygous (one copy of) Rose Comb looks identical to the homozygous (two copies of) rose comb. Here, heterozgyous is shortened to just 'het. RC'.
Rose comb x Rose Comb = 100% rose comb.
Rose comb x Single Comb = 100% het. RC
Rose Comb x het. RC = 50% Rose Comb, 50% het RC
het. RC x het RC = 25% Rose Comb, 50% het RC, 25% single comb
het. RC x Single Comb = 50% het. RC, 50% Single Comb
Rose Comb x Pea Comb = 100% het. Walnut Comb
References & Further Reading
Shen M, Qu L, Ma M, Dou T, Lu J, Guo J, et al. (2016) Genome-Wide Association Studies for Comb Traits in Chickens. PLoS ONE 11(7): e0159081. https://doi.org/10.1371/journal.pone.0159081
Bateson, W., Saunders, E. R., Punnett, R. C., & Hurst, C. C. (1905). Reports to the Evolutionary Committee of the Royal Society (Report II.–Experimental studies in the physiology of heredity & Experiments with poultry). Royal Society, London.
American Poultry Association. (2023). American Standard of Perfection (45th ed.)
Imsland, F., Feng, C., Boije, H., Bed'Hom, B., Fillon, V., Dorshorst, B., ... & Andersson, L. (2012). The Rose-comb mutation in chickens constitutes a structural rearrangement causing both altered comb morphology and defective sperm motility. PLoS genetics, 8(6), e1002775.
Crawford, R. D., & Merritt, E. S. (1963). The relationship between rose comb and reproduction in the domestic fowl. Canadian Journal of Genetics and Cytology, 5(1), 89-95.
Wang, Y., Li, J., Feng, C., Zhao, Y., Hu, X., & Li, N. (2017). Transcriptome analysis of comb and testis from Rose-comb Silky chicken (R1/R1) and Beijing Fatty wild type chicken (r/r). Poultry Science, 96(6), 1866-1873.
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