Description:
The combless gene (sometimes called the Breda gene) in chickens causes the bird to have a completely absent comb in females and almost absent comb in males - short of two small stubs by the beak (2). It is a completely recessive gene, and works on top of the duplex-V comb and rose comb genes (1). It is unknown how this gene works on top of the wildtype single comb or the duplex buttercup combs.
Overall, it is an under-studied gene in chickens with minimal information because of the rarity of combless birds. The only breed without a comb is the Breda fowl, which displays the combless gene on top of the duplex and possibly rose comb (1), and is no longer included into the APA Standard of Perfection due to general breed activity.
The gene does still exist in the United States, with a group of several breeders working to bring the Breda back into the showroom.
Breeding with Combless:
Combless x Combless = 100% Combless
Combless x Duplex Rose Comb = 100% Combless Carriers (They look like simple Duplex combs)
Combless x Combless Carrier = 50% Combless, 50% Combless Carriers
Combless Carrier x Combless Carrier = 25% Combless, 50% Combless Carrier, 25% Duplex Rose Comb
Combless Carrier x Duplex Rose Comb = 50% Combless Carrier, 50% Duplex Rose Comb
Combless x Single Comb = 100% Large Duplex Comb
References & Further Reading
Torres, Juan P. "A Review of Mendelism in Domestic Fowls..." (1926).
Somes, Ralph G. Jr., "International Registry of Poultry Genetic Stocks" (1988). Storrs Agricultural Experiment Station. 29. https://digitalcommons.lib.uconn.edu/saes/29
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