DOSAGE EFFECT OF THE SPELTA GENE q OF HEXAPLOID WHEAT

Abstract

When present in up to four doses, q behaves as a null allele, but five doses result in squareheaded-ness and six in more compact spikes. Thus q is not a deficiency or an amorph but an active gene, suggesting that ssp. spelta did not originate from ssp. vulgare in the way that speltoids have been obtained more recently. The genes q and Q are hypomorphic and hypermorphic to each other, respectively, five doses of q being equivalent to about two doses of Q. "Gene q has less spelting effect than does deficiency for the Q-locus. Q-locus deficiency results in speltoidy in ssp. vulgare, while in ssp. spelta it presumably gives rise to a more extreme spelta phenotype. The allele q can cause either speltoid or spelta depending on the background." The expression of the gene is discussed in relation to pleiotropy and the modifying effect of the genetic background.