PHENOMENA OF INHERITANCE 



and the other round pollen. But when these were crossed a remarkable 

 thing occurred, for the progeny, "instead of being white, were purple, 

 like the wild Sicilian plant from which our cultivated sweet peas are 

 descended." This is apparently a typical case of reversion and its 

 cause was found in the fact that at least two factors are necessary in 

 this case for the production of color, a pigment factor R and a color 

 developer C. One of these was lacking in each of the white parents, 

 their gametic formula? being Cr and cR, but when these two factors 

 came together in the offspring a purple-flowered type was produced 

 with the gametic formula Cc Rr. These F 3 plants produced colored 

 and white F 3 plants in the proportion of 9 colored : 7 white and the 

 colored forms were of six different kinds (Fig. 57). For the produc- 

 tion of these six colored forms 

 five different factors must be 

 present in the gametes, according 

 to Punnett, viz.: (1) a color base " 

 (22), (2) a color developer C, (3) 

 a purple factor B, (4) a light p 1 

 wing factor L, (5) a factor for 

 intense color I. When all of 

 these factors are present the re- Fz 

 suit 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 dif- 

 ferent factors may be involved in 

 producing the coat colors of rab- 

 bits ; these are : 



C a common color factor neces- 

 sary to produce any color. 

 B a factor acting on C to pro- 

 duce black. 

 Br a factor acting on C to pro- 

 duce brown. 

 Y a factor acting on C to pro- 

 duce 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, below which is a band of yellow, while the basal part 

 of the hair is grav. 



^7 



Fig. 57. Results of Crossing two 

 Different Races (A) and (B) of White 

 Sweet Peas/ all the F x hybrids (C) are 

 purple with blue wings like the wild ances- 

 tral stock ; in F 2 six colored varieties are 

 formed ranging from purple with blue wings 

 (D) to tinged white (7) and several kinds 

 (genotypes) of white varieties (A'). 

 (After Punnett.) 



