O. A. Merritt Hawkes 271 



Consideration must be now given to the possibility that S is some- 

 times a heterozygous form. The six matings S x (A . or B) produced 

 15 X and 9 of the other types, a very large proportion of L, unless S is 

 sometimes heterozygous or unless the L fector is what may be described 

 as an excessive dominant, and the matings L x S hy no means indicate 

 that. In this connection the family in Fig. 6, Tree H, (i), is interesting, 

 where the mating S ^ x A j* produced two male L. Now this female 

 S may be a heterozygote, being the child of the mating L ^f x S $ , or 

 the two male L of generation three may themselves be heterozygotes, a 

 point which can only be settled during the next decade. This may be 

 a case in which the heterozygote appears as an S because it is a 

 female. 



There is certainly a sex factor in the S type and this may be 

 accounted for by the existence of certain female heterozygotes appearing 

 as S type ; on the contrary, there may be a tendency for the male 

 heterozygote to appear as an L. It is possible that a comparison of the 

 matings L ^ with ^, i^ or >S», and L % with A,B ov ^, may throw some 

 light on the sex difference. Of the former, there are 34 matings, 

 producing 72 X, 14 >Sf, 13 ^ and B,oy12 L type to 27 of the other types, 

 a proportion of 16 : 6. Of the latter (X % with A, B or 8) there are 22 

 matings producing 70 X, 9 S, 10 A and B, or 70 X to 19 other types 

 or approximately 23 : 6. These results suggest at once that more male 

 than female X are heterozygotes. Reference must here be made to Fig. 6, 

 Tree G, in which it is the female X which appears heterozygous rather 

 than the male X. 



The above results must be controlled by an enquiry into the proportion 

 of the sexes in the groups of offspring arising from the above two gi^oups 

 of matings. In both cases the A and B types will not be counted as 

 they show no sex difference. 



The mating X ^ x{A, B or 8) produces 86 X and S olBTspring, 

 divided thus: X, 35 ^ and 37 % ', 8, Z J" and 11 ?, i.e. (/:?:: 3:4, 

 and there are 19*4 per cent, of >Sf type. 



The mating X $ x{A,B or 8) produces 79 X and 8 offspring divided 

 thus: X, 29 ^Z" and 41 $ ; ,Sf, 4 c/* and 5 ? , i.e. c/" : ? :: 3 : 4, and there 

 are 12-8 per cent, oi 8 type. 



The sexes in both cases are approximately the same, but a larger 

 proportion of 8 is produced where the X parent is male rather than 

 female. Thus, the above deduction is confirmed, that when the X type 

 is heterozygous, it is moi-e frequently male than female. 



