The present paper is an attempt to give a quantitative description of one of the important relationships postulated by conditioned-response theories of learning. An extensive experimental literature, comprehensively reviewed by Hilgard (2), points to the essential similarity between 'reward' learning and 'reinforcement' learning, suggesting the possibility of deriving both types from a single set of postulates. Hull (5, 6) has attempted the theoretical derivation of a large number of the mechanisms of adaptive behavior, notably those of trial-and-error learning, from postulates based on a number of the phenomena found in conditioning. The predictive value of such a theoretical system depends in large part on a knowledge of the quantitative nature of the phenomena in question, particularly reinforcement, extinction, and spontaneous recovery.The strength of a response tendency as some function of the amount of reinforcement given it, is a relationship whose determination is dependent on the method used for testing the strength of the tendency. The most commonly used indicators are: magnitude of response, frequency of appearance of response, latency of response, and the resistance of the response to experimental extinction. The last mentioned measure was suggested by the following statement of Pavlov (7): "... The greater the intensity of the excitatory process, the more intense must be the inhibitory process to overcome it, and therefore the greater number of unreinforced repetitions necessary to bring about complete extinction" (p. 61).1 This investigation is a part of a coordinated research program of the Institute of Human Relations, Yale University. It was carried out under the direction of Professor Clark L. Hull, to whom the writer is greatly indebted for interest and assistance in the problem.

The β-, γ- and δ-kafirin genes were sequenced from 35 Sorghum genotypes to investigate the allelic diversity of seed storage proteins. A range of grain sorghums, including inbred parents from internationally diverse breeding programs and landraces, and three wild Sorghum relatives were selected to encompass an extensive array of improved and unimproved germplasm in the Eusorghum. A single locus exists for each of the expressed kafirin-encoding genes, unlike the multigenic α-kafirins. Significant diversity was found for each locus, with the cysteine-rich β-kafirin having four alleles, including the first natural null mutant reported for this prolamin subfamily. This allele contains a frame shift insertion at +206 resulting in a premature stop codon. SDS-PAGE revealed that lines with this allele do not produce β-kafirin. An analysis of flour viscosity reveals that these β-kafirin null lines have a difference in grain quality, with significantly lower viscosity observed over the entire Rapid ViscoAnalyser time course. There was less diversity at the protein level within the cysteine-rich γ-kafirin, with only two alleles in the cultivated sorghums. There were only two alleles for the δ-kafirin locus among the S. bicolor germplasm, with one allele encoding ten extra amino acids, of which five were methionine residues, with an additional methionine resulting from a nucleotide substitution. This longer allele encodes a protein with 19.1% methionine. The Asian species, S. propinquum, had distinct alleles for all three kafirin genes. We found no evidence for selection on the three kafirin genes during sorghum domestication even though the δ-kafirin locus displayed comparatively low genetic variation. This study has identified genetic diversity in all single copy seed storage protein genes, including a null mutant for β-kafirin in Sorghum.

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