700 General and Applied Biology 



human traits show absolute Y Hnkage (do not appear in females and are 

 not transmitted to them). An example is the so-called "porcupine man" 

 trait (bristly, scaly skin) which appears in males only. Another possible 

 Y-linked inheritance is a special type of web toe (web skin between 

 second and third toes). It is known that a diflferent web toe condition 

 exists which is present in both males and females, with a preponderance 



Fig. 345. — Sex-linked inheritance in the fruit fly (Drosophila sp.). The red- 

 eyed male (upper right) and the white-eyed female (upper left) are crossed to 

 produce the male and female of the Fi generation. The factor {W) for red eyes 

 is carried in the X chromosome of the male, while the curved male Y chromosome 

 does not carry an eye-color factor. The factor {w) for white eyes is carried in 

 the X chromosome of the female. When members of the Fi generation are crossed, 

 the four kinds of the Fo generation are produced (lower group). Note that a 

 male has a larger tip of black on his abdomen than the female. Contrast these 

 results with those in Fig. 346. (From Morgan: Evolution and Genetics, Prince- 

 ton University Press.) 



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