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THE AMERICAN NATURALIST [Vol. L 



"P" having a value .862 means that, in nearly nine cases out of 

 ten, other random samplings would deviate more widely from 

 the theoretical. 



The critical test as to whether or not congenital cataract can 

 be considered as a simple recessive character lies in the matings 

 of abnormal by abnormal. Families of this kind should have 

 only abnormal children. Only three such matings are avail- 

 able. In two of these, five and two children, respectively, are 

 the total numbers produced; and these are all abnormal. The 

 other case is a doubtful one. Both parents are classified as hav- 

 ing discoid cataract ; one is given as seriously affected, the other 

 only slightly so. Seven children are given for this mating : two 

 are abnormal, and the others apparently normal. Three of these 

 five died in infancy, so that their classification is doubtful, but 

 there is no question as to the others. Assuming, as Bateson does 

 in his cases, that there has been a faulty classification of the 

 parents, that the parent given as slightly affected is not con- 

 genially defective, but adventitiously so early in life ; then this 

 one discrepancy might be conveniently overlooked. 



Another explanation may be found, however, in the fact that 

 heterozygous individuals sometimes show the recessive character. 

 Cases are known where a small percentage of heterozygous indi- 

 viduals show the recessive character, although the homozygous 

 and heterozygous dominants are generally indistinguishable. 

 If such is the case here, the slightly affected parent is hetero- 

 zygous, and the occurrence of normal children is expected. 



This assumption also helps to explain the deviation of observed 

 results above the theoretical in Table I, and their deviation 

 below the theoretical in Table II. If heterozygous individuals 

 are sometimes classified as recessives, it would affect the classi- 

 fication of both the parents and the children. A few matings 

 of abnormal (heterozygote showing the recessive character) by 

 normal would be included in the category B which rightfully 

 belong in category A. Thus matings giving a one-to-three ratio 

 would be included among matings giving a one-to-one ratio. This 

 would tend to reduce the observed results below the expected. 

 A faulty classification of the children would tend to raise the 

 results, but this would not be as strong a deviating factor as 

 when influencing the parents and therefore a number of chil- 

 dren. Thus the balance would tend slightly toward a decrease 

 in the regular expectancy ; a result which fits well with that ob- 

 tained in Table II. 



