paramutation; B1 Paramutation at the B1 locus: (Coe 1966). The phenomenon through which a spontaneously occurring weak B1 allele (B1'), when in a heterozygote with the standard B1 allele, causes B1 to change regularly to the B1' form. The cobs shown are the Pl1 and p=wr (red cob). Those with standard B1 are on the right; with B1' on the left.