Non so se ci sono degli studi nuovi ma da ciò che leggo, sembra che non ci sia differenza tra eb e ebc, quindi in tal caso ebc non esiste ma si tratta sempre di eb. Leggi qua:
The following is direct quote from Dr Okimoto on the DNA sequencing of E locus allele from the Silician Buttercup breed, by Leif Anderson. This indicates that the Buttercup pattern may be produced with the eb allele in combination with other modifying genes, and that the ebc allele had not been sequenced.
Dr Ron Okimoto (quote from The Classroom @ The Coop) ......." Leif Andersen has sequenced the buttercup allele (ebc) and it is the identical sequence to the eb alleles that I've sequenced in Partridge Rocks and the Smyth Brown line. If there is a difference between the alleles it is in the regulation of the gene and not in the coding sequence. There may be linked genes that affect the expression of the E locus too."
(Link:
www.edelras.nl/chickengenetics/pdf/Poultry_Genetics_for_Exhibition_Bree... )