270 



First and Second Toes in Man 



Only 6 matings & v. A and S x B were recorded, these produced 24 

 offspring, 15 L, *7 S, 2 A and B, or 15 L type and 9 of the other types. 

 Again there is dominance of the L type, but the proportion, 15 : 9, 

 indicates a very real genetic difference between this type of mating and 

 L X (A or B) in which the offspring are as 3f : 1 or 15 : 4. 



The five remaining matings between A and B types gave only 6 

 offspring, 5 L and 1 A, the L factor being preponderatingly dominant. 

 The behaviour of A and B with one another and with S and L respec- 

 tively, makes it clear that they are heterozygous types, just as the 

 matings L x L and S x S show that these are generally pure types for 

 the character under consideration. 



The net result of all these groupings is to show that the L toe-type 

 is the dominant, the dominance being, so far as yet determined, irregular. 

 The usual heterozj^gous forms are A and B, but some L types also 

 behave as heterozygotes. That L may be both a hetero- and a homo- 

 zygote is seen from Fig. 6, Tree G. 



FIGURE 6. 

 Tree G. 



1. 



(i) I 

 ? = c? 

 L I B 



l(ii) 



? = ^ 

 A I L 



— I 1 1 1 I 1 1 1 r n 



I I X\ I I I /\ i I i .! 



BLSLSLLLSLLLLLLLLL 



Two generations to show the two values of L. Amongst the offspring are 

 three pairs of ordinary twins. 



1. 



Tree //. 



-n (i) r- 



I i 



,S' I A 



r--+- 

 I I 



I 1 



I I 



L L 



6 = 9 



A L >V L I 



I — I — I .1 — r^ 



Three generations. 



