EUGENICS RECORD OFFICE. 149 



Dr. Corner during the summer, and he has been able to establish the 

 fact that there is in hogs an internal migration of ova from one horn of 

 the uterus to another. He finds also a strong tendency, through this 

 mechanism, to establish an approximate equality of embryos in the 

 two horns, even when the disparity in the number of corpora lutea in 

 the ovaries is very great. 



SEX-LINKED LETHAL FACTORS IN MAN. 



Dr. C. C. Little, with the cooperation of Miss Marion Gibbons, has 

 prepared for press a paper on the statistical evidence of the occurrence 

 of sex-linked lethal factors in man. 



Sex-linked factors, other than lethals, have long been known in man. 

 Among these, two genes which have been especially well studied are 

 those for hemophilia and for color-blindness. The genes for these 

 characters and their normal allelomorphs are carried in the X or sex 

 chromosome. Since sex-linked lethals if they exist will also be carried 

 in the sex-chromosome, certain of them may be closely linked with 

 either of these genes or with their normal allelomorphs, according to 

 the nature of the gamete in which they originate. If one of them 

 occurs in a chromosome in which the gene for hemophilia is carried, it 

 will, if it be closely linked with that gene, eliminate all the males, which 

 would otherwise be hemophilic except in case a cross-over occurred. 

 The same is true for color-blindness. Families in which such a con- 

 dition was found might continue for several generations without 

 giving a hemophilic or color-blind individual because of rareness of 

 cross-overs. Such families would, therefore, not be recognized and 

 would not be included among those selected to show the method of 

 inheritance of these traits. 



If, however, the lethal factor were linked with the normal allelo- 

 morph of these genes, normal sons would appear only when crossing- 

 over occurred. These families would show a striking excess of hemo- 

 philic or color-blind males, as the case might be, and would, of course, 

 be included in any study of the inheritance of these traits which might 

 be made with other families in which no sex-linked lethals occurred. 

 If a sufficient number of such families were, by chance, included in any 

 mass of statistics on the inheritance of these traits, they should pro- 

 duce in the data a significant excess of hemophilic or color-blind males 

 above the expected 1 :1 ratio. 



To test this matter, data at the Eugenics Record Office, as well as in 

 Bulloch and Fildes's work on hemophilia and in Nettleship's work on 

 color-blindness, have been tabulated and analyzed. Dr. Sewall 

 Wright had previously tabulated the data in Bulloch and Fildes, and 

 his data, which have very kindly been turned over to Dr. Little, are 

 included in his figures. He has developed also a formula for calculating 

 the number of abnormals (bleeders or color-blind) to be expected on 



