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THE AMERICAN NATURALIST 



[Vol. L 



them. They are however hardly necessary since the numbers 

 ninety-six and forty-seven upon which Danforth bases his criti- 

 cism are too small to make a really critical comparison. 



Since the number of affected F x individuals which should give 

 one half affected children exceeds the number of unaffected F x 

 individuals which should have only one third affected children, 

 the actual number of affected children in the two kinds of F 2 

 populations would deviate proportionally farther from a ratio 

 of one to two. If it is conceded that the chances for the two 

 kinds of matings are not equal, then this deviation would be 

 expected. 



The three cases in category C which we gave as matings of 

 abnormal by abnormal which theoretically should give only ab- 

 normal children according to the simple recessive hypothesis can 

 be found in Harman's tables in the "Treasury of Human In- 

 heritance " 5 as follows: Table 309, Parents I, 1 and 2— Children 

 II, 1 to 5; Table 312, Parents II, 3 and 5— Children III, 3 to 4; 

 and Table 342, Parents III, 28 and 37— Children IV, 60 to 66. 

 Danforth says that he can find only two of these. They are 

 probably 309 and 342. The one which occurs in Table 312 

 should not have been used without an explanation. Although 

 the chart indicates that both parents are affected as well as their 

 two children, the description of the family shows that the exact 

 parentage is somewhat in doubt. It was an error on our part 

 not to mention this fact. 



v With regard to the family in 342 in which part of the children 

 are normal where only abnormals are expected, Danforth does 

 not accept our explanation that heterozygotes sometimes have the 

 recessive character. This is quite frequently shown in other 

 material. His refusal to accept this explanation to account for 

 the one exception to the recessive hypothesis is shown in the fol- 

 lowing quotation: "a single bona fide case in which two affected 

 individuals produce normal offspring is sufficient to overthrow 

 it" (the recessive hypothesis) (p. 447). We can not under- 

 stand his refusal to accept this explanation to account for one 

 exception when he is willing to use it to explain thirty-one excep- 

 tions to the dominant hypothesis ! This is evident from the fol- 

 lowing quotation previously alluded to: 



Again, since Jones and Mason elsewhere in the same paper (p. 124) 



tory Memoirs, XI, Part 4, Section XUIa, pp. 12^-169, PI. XXVIII- 

 XXXIII, Dulau and Co., London, 1910. 



