271 



PHENOMENA OF INHERITANCE 



they may appear in either sex though they are 

 usually transmitted from fathers to daughters, 

 or from mothers to sons ("criss-cross" inheri- 

 tance) in exactly the way in which the sex 

 chromosomes {X) are transmitted. Morgan 

 has therefore concluded that the factors for 



Flies 



XX M X0 m Fz 



Fig. 59. Sex-linked inheritance of white and red eyes in 

 Drosophila. Parents, white-eyed male and red-eyed female; 

 Fj, red-eyed males and females; F^, red-eyed females and equal 

 nmnbers of red-eyed and white-eyed males. The distribution 

 of sex chromosomes is shown to right of flies; X carries the 

 factor for red eyes, ]^ the factor for white eyes, @ stands for 

 absence of X- (After Morgan.) 



