The progress of Genetics since the rediscovery of Mendel's papers. 



403 



Wood (117) found on crossing Dorset sheep (horned in both sexes; 

 mth Sulfolks (hornless in both sexes), that horns were dominant in 

 males, recessive in females. In F., there were horned males and 



C 



D 



Fig:, l?- Four types of lambs in F., from the cross Dorset Horn X hornless Suffolk. 



A horned c/'; B hornless c/'; C hornless 9; D horned $. (From Wood. Tlie parent? 



and Fl type are figured in the original paper.) 



females, and hornless males and females. These hornless males and 

 the horned females will doubtless prove to be pure to their respective 

 types (Fig. 17). 



Such a distribution is somewhat like what is seen in the case 

 of a sex-limited disease. In these cases the peculiarity is manifested 

 generali}^, though not always, by members of one sex, say the male ; but 

 the females, though unaffected themselves, may transmit it to their 

 male offspring. Haemophilia and colour-blindness are the most famous 

 examples of this "Knight's move" descent, as it may be called. 



Clearly there is a general resemblance to the phenomenon seen 

 in the sheep. If the affected sex is the male, the unaffected males 

 do not transmit the condition, though the unaffected females'^) maj' 

 do so. We may suppose that the unaffected males are by segregation 



^) The popular belief that such a condition is transmitted by females only, is 

 of course a mistake. In haemophila, for example, there are many instances of trans- 

 mission by affected males. 



