216 



Biology in America 



tional evidence for the cliromosome hypothesis as outlined 

 a])()ve. 



In the course of their experiments tlie students of the fruit 

 fly were suddenly confronted with an unexpected, and at 

 first sight unexplaiiuihle case, which seemingly set the chromo- 

 some hypothesis on its head. As already explained, if a pure 



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Chromosome ATap Hhowing Distkiiuition of Linked Characters in 



The Fruit Fly 

 After Morgan, "Heretlity and Sex." 

 By permission of the Columbia University Press. 



white-eyed female be mated to a red-eyed male, red-eyed 

 daughters and white-eyed sons in approximately equal num- 

 bers are the result. But in one set of experiments this cross 

 produced, in addition to the expected classes of . offspring, 

 about 2.5% of white-eyed females and an equal number of 

 red-eyed males. Such a result is readily explainable how- 

 ever "on the assumption that the two X chromosomes of the 



