CHROMOSOMES AND GENES 



57 



chromosomes. The diagram gives the expected results 

 when such a female is fertilized. By good fortune the 

 X-chromosomes that became attached carried each the 

 recessive gene for yellow wings. The presence of the two 



Double-X yellow by 



rtl9 



Y + 



Wild 



l%6 



Y 



Fig. 37. 

 Diagram illustrating the fertilization of the two kinds of eggs of 

 an attached, XX, yellow female (whose double X-chromosome is 

 represented here in solid black) by wild type male. There is a 

 Y-chromosome in the double-X female. It is represented here by 

 cross-hatching. The Y-chromosome in the male is indicated in the 

 same way. After reduction two kinds of eggs are present (see 

 above to left). These fertilized by the two kinds of spermatozoa 

 of the normal (wild type) male (see above to right) give the four 

 classes at the bottom of the diagram. 



