TYPES OF MENDELIAN HEREDITY 37 



There is a third kind of white race of poultry, 

 namely, white Leghorn, in which white is dominant. 

 Crossed to colored birds the offspring are white 

 (with often a few colored feathers, which indicates 

 that dominance is not complete). 



In the silkworm also a dominant white and a reces- 

 sive white factor have been found. The genetic 

 results are comparable in all respects to those in the 



fowl. 



There are also cases of blacks or melanic types, 

 that have different factorial bases. There are three 

 black races of Drosophila — called sable, black, and 

 ebony — that belong respectively to the first, second, 

 and third groups. These are much alike, but close 

 scrutiny reveals shght differences. Any two crossed 

 together give gray Fi flies. 



There are three pink eye colors in Drosophila, one 

 w^hose locus is in the third chromosome (pink), and 

 two sex hnked eye colors which are so similar that no 

 certain difference between them can be observed. 



Not only pigment but also structural characters 

 may parallel each other in a remarkable manner. For 

 example, in Drosophila the mutant stocks ''bow" 

 (sex linked) and ''arc" (II chromosome) have wings 

 that curve evenly downward over the abdomen. 

 Ther§ are also two kinds of flies whose wings turn 

 up sharply near the ends. These stocks are "jaunty " 

 (second chromosome) and "jaunty I," which is sex 

 linked. Two types, called ' 'fringed ' ' (II chromosome) 

 and "spread" (III chromosome) , are characterized 

 by thin textured wings held out nearly at right 



