Color-blind 

 male 





Zygotes 



Color-blind 

 female 



COLOR BLINDNESS LINKED TO MALENESS IN MAN 



To understand why color blindness is generally found only in males, we assume that 

 it is determined by a recessive factor in the X-chromosome. If the affected X com- 

 bines with a normal X, the recessive character does not show. A female would be 

 color-blind only with two affected X-chromosomes — that is, if she were the daughter 

 of a color-blind man and of a normal woman whose father or grandfather was also 

 color-blind 



results from the interacting of many elements or factors from several genes 

 being present together, often in separate chromosomes. An interesting ex- 

 ample of these ideas is seen in the commercial production of "Silver Fox" 

 furs (see illustration, p. 495). 



Two distinct mutations have occurred among the foxes, both producing 

 a black, or silver, fur; and both breed true. The Standard Black, as it is 

 called, originated in Eastern Canada; the Alaskan Black, in Alaska. Both 



493 



