102 Heredity and Environment 



five different factors must be present in the gametes, according 

 to Punnett, viz.: (i) a color base R, (2) a color developer C, 

 (3) a purple factor P, (4) a light wing factor L, (5) a factor for 

 intense color /. When all of these factors are* present the result 

 is the purple wild form with blue wings, while the omission of 

 one or more of these factors leads to the production of six 

 forms of colored and various types of white-flowered plants of 

 the F 2 generation. 



Castle found that eight different factors may be involved in 

 producing the coat colors of rabbits : these are : 



C a common color factor necessary to produce any color. 



B a factor acting on C to produce black. 



Br a factor acting on C to produce brown. 



Y a factor acting on C to produce yellow. 



I a factor which determines intensity of color. 



U a factor which determines uniformity of color. 



A a factor for agouti, or wild gray pattern, in which the tip of 

 every hair is black, its middle yellow, its basal part gray. 



E a factor for the extension of black or brown but not of 

 yellow. 



t 



Plate found that all of these factors except the last, E, are also 

 involved in the production of the coat colors of mice. Baur has 

 recognized more than twenty different factors for the color and 

 form of flowers in the snapdragon, Antirrhinum. 



Modifying Factors. — Morgan and Bridges have found that the 

 effects of many factors may be modified by other factors. Thus 

 the eye color of Drosophila known as "eosin" may be modified by 

 six or seven different factors, occupying different loci in the 

 chromosomes, one of which intensifies "eosin" while the others 

 dilute it. These modifying factors are undoubtedly like other 

 Mendelian factors in their behavior and they show that an adult 

 character may be the result of several different inheritance fac- 

 tors. Indeed Morgan says "that an overstatement that each fac- 



