Flies 



Cellular Basis 



Chromosomes 



Parents 



Gametes 



cf ? 



K / rf 



Gametes 





? .9 c? <5 



FIG. 62. RECIPROCAL CROSS OF FIG. 61. Parents, white-eyed $ and red- 

 eyed $ ; Fi t red-eyed 9 and white-eyed $ ("criss-cross inheritance") ; 

 F 2 , equal numbers of red-eyed 9 and $ and white-eyed $ and $ . The 

 distribution of the sex-chromosomes is shown on the right, as in Fig. 59. 

 (After Morgan.) 



acters and has even indicated the relative positions of different 

 genes in the chromosomes. 



Thanks to the work of Bateson, Morgan, and their associates, it 

 is now known that many characters are linked together in inheri- 

 tance. Darwin had long ago noted that male albino cats with blue 

 eyes are usually deaf and many other cases of the association of 

 peculiar characters had been reported by earlier observers. In 

 1906, Bateson and Punnett found that sweet peas with purple 

 flowers usually have elongated pollen grains, whereas those with 

 red flowers have round pollen. Since 1910 Morgan and his pu- 

 pils have discovered more than one hundred new characters, or 

 mutations in the fruit fly, Drosophila melon og aster, which are 

 linked together in four groups. 



a. Sex-linked Inheritance. The first cases of such linkage 



