3*4 



THE QUARTERLY REVIEW OF BIOLOGY 



of this series No. 4 is certainly a quanti- 

 tative condition of B u No. 6 of B 2 , and 

 No. 5 of B x and jB 2 . Therefore the differ- 

 ence between £1 and B 2 ought to be 

 quantitative. If this is the case all the 

 possible combinations of z, 3, 4 quantities 

 of jBi and 5 2 must form parallel series to 

 the homozygous series, which is the case. 

 Finally the gene B with all its combina- 

 tions falls exactly in line in these different 

 series and therefore must also be regarded 

 as belonging to the series of quantities. 

 In other words, there is a number of 

 different equations involving B, Bi, B 2 , 

 which can be solved only if B, B u B 2 have 

 typical but different numerical values. 



Thus we regard this case as conclusive 

 proof of the quantitative nature of 

 multiple allelomorphs. Our second result 

 was that these different quantities of a 

 gene are linked with reactions proceeding 

 at different rates proportional to the 

 respective quantities which produce the 

 typically different phenotypical result. 

 The present writer has analyzed this case 

 in the same direction and found that the 

 results can best be represented this way. 

 (For details see Goldschmidt, \ja., p. 63 

 ff. It ought to be mentioned that on 

 p. 68, 69, of the work in question a lapsus 

 calami occurred. The tables on these 

 pages have erroneously been calculated as 

 differences instead of as proportions. If 

 corrected the similarity between result 

 and calculation is still better.) 



In concluding this section a general 

 point may be mentioned shortly. Many 

 years ago Baur in discussing our views 

 in regard to the quantity of the gene 

 remarked that it is impossible to imagine 

 that the genes are always present in the 

 same quantity. Lillie Q-vf) has recently 

 taken up the same argument. Speaking 

 of possibilities I might venture the opinion 

 that if chromosomes were invisible bodies 

 and their numerical constancy only 



deduced from genetic experiments, the 

 same argument would immediately be at 

 hand. The same applies to every numer- 

 ical constancy in organisms, the segments 

 of insects and the number of cells in the 

 nervous system of Ascaris. I cannot see 

 why it is more difficult to conceive a 

 typical number of molecules for a given 

 gene. But finally these considerations are 

 superfluous because it is an actual fact that 

 the effect of a gene is different and typical 

 if present in 1, z, 3, 4 quantities, which 

 would be hard to account for if the unit 

 quantity was not of fixed magnitude. 



B. THE EFFECTS OF THE SAME GENE IN DIF- 

 FERENT QUANTITIES IF MORE THAN 

 ONE GENE IS INVOLVED 



Genes in different quantities may also 

 be studied in cases of either absence or 

 multiplication of parts of chromosomes, 

 of whole chromosomes, or of whole 

 chromosome sets. In such cases, how- 

 ever, the conclusions are subject to 

 uncontrollable error. The result attrib- 

 uted to different quantities of one gene 

 may be decisively influenced by the 

 corresponding difference in many or all 

 the other genes. If whole chromosomes 

 or even whole chromosome sets are 

 involved the additional effect of the 

 change of the nucleo-plasmic ratio may 

 come into play. Thus experiments of this 

 type can only furnish additional evidence, 

 which has to be handled cautiously, 

 weighing the different possibilities for 

 each case. 



The smallest deviation from the single 

 gene evidence is obtained if only a small 

 number of genes are involved, as in the 

 deficiency studies of the Drosophila 

 workers. After Bridges has shown that 

 the effects of the deficiency are of the 

 same order as in the haplo IV, one can 

 safely assume that deficiencies are real 

 absences or at least complete inactivations 



