414 



C. C. HURST 



On the basis of these predictions the present L. F. and R. F. data show 31 

 offspring of unexpected grades out of a total number of 1370 offspring, or 2.2 

 per cent exceptions. 



In the Leicestershire families there is only one exception in 812 offspring, 

 where a grade 2 appeared instead of the grade 3 expected. In the Royal 



TABLE 2 

 Genelical formula for intellect 



Nn + (Aa + Bb + Cc + Dd + Ee) with 729 genotypes 

 N and n are a major pair of genes for typical and atypical intellect. 

 Dominant N (NN or Nn) determines typical mediocre intellect of grade 5. 

 Recessive nn determines atypical intellect of various grades 0-10. 

 Aa. . .Ee are minor pairs of modifying genes which produce grades 0-10. 

 Dominant modifiers A . . . E act as equal and cumulative increasers of grades. 

 Recessive modifiers a . . . e act as decreasers. 

 With nn the modifiers are fully active. 

 With NN the modifiers are totally inactive. 

 With Nn the modifiers are inactive or only partially active. 

 Thus the 729 genotypes produce seven kinds of effective gametes. 



* Inactive. 



families there are 30 exceptions in 558 offspring, or 5.3 per cent of unexpected 

 grades. Since these occur in batches in a very few families it is highly prob- 

 able that they are due to errors in parental gradings. Woods' gradings are 

 adopted as they stand and no attempt has been made to examine them criti- 

 cally, so that the independent value of the data has been preserved. 



