PHYSICAL CHARACTERS IN MAN 115 



these records and added later ones, making; ten 

 generations. The night-blinchiess was first broiii^ht 

 to the village by Jean Nougaret, who was born 

 about 1637. It has therefore been handed down for 

 about 250 years through a large number of indi- 

 viduals. Bateson (1909, p. 220) gives a chart of this 

 pedigree. 



In another family studied b}* Newman (191 3), 

 night-blindness (hemeralopia) is inherited like colour- 

 blindness, as a sex-linked character, being transmitted 

 through unaffected daughters of affected males to 

 some of their sons. This family is from Texas, having 

 originated in North Carolina. In one respect it 

 departs from the t3^pical scheme for sex-linked in- 

 heritance, in that there is " apparent non-inheritance 

 of the capacity to transmit night-blindness on the 

 part of the sisters of night-blind men." In F3 and 

 F5, if there were no consanguineous marriages, there 

 should be equal numbers of females carrying or not 

 carrying night-blindness. But none of the five 

 married sisters of F3 night-blind men show any 

 trace of night-blindness in their progeny. Newman 

 suggests that possibly night-blindness cannot be 

 inherited through two successive generations in the 

 female line, owing to prolonged association of the 

 defective X (sex) chromosome with a normal X. 

 The next generation will determine whether this is 

 the true explanation. 



In its main essentials the character in this familv 

 behaves as a recessive located in the X chromosome, 

 but, as in haemophilia, there is an excess of abnormals. 

 Thus, of the 36 offspring of the night-blind-carrying 

 daughters of night-blind men, there were 22 (j", 14? , 

 and of these 22, 17 were affected and only 5 not. In 

 this family the night-blindness is usually accompanied 

 by m3^opia (short-sightedness), and almost invari- 

 ably by strabismus (squinting), Avith frequent occur- 



