602 Journal of Agricultural Research vol. xx.No. 8 



modes — red, yellow, lemon, and cream, given in the order of most intense 

 to most dilute. Those classified as "cream" were, when adults, a very 

 light straw color, almost white. The 23 F 2 individuals were distributed 

 as follows: 6 red, 9 yellow, 2 lemon, and 6 cream. It is not certain 

 that yellow and lemon belong to two genetically distinct classes. There 

 is little difference between them. If we group yellow and lemon together 

 as an intermediate shade, the ratio of 6 intense, 11 intermediates, and 

 6 dilutes suggests a 1:2:1 ratio; but this is probably a coincidence, and 

 we can not infer a single allelomorphic pair of factors for intensity and 

 dilution with incomplete dominance, as later experiments will show. We 

 do not know what the calculated ratio for the various shades of red in 

 such an F 2 population should be, for we do not know the genetic consti- 

 tution of each F t female or the Duroc-Jersey male with regard to these 

 diluters of red. This one fact, however, is clear — there was marked seg- 

 regation in shades of red in the F 2 generation. Plate 70 shows some of 

 the variation in the intensity of red. 



In order to test these dilute conditions, 9 2e, an F 2 yellow, and 9 2f, 

 an F 2 lemon, were mated to S 3f, an F 2 yellow. It was thought that if 

 yellow and lemon were intermediate conditions between cream and red, 

 then these matings would give a range of forms from red to cream. 

 Female 2e gave 5 F 3 offspring classified as red. They were discarded, 

 and unfortunately some doubt exists as to the exact shade of red. The 

 shade of red deepens as the animals grow older. We are quite sure they 

 were not cream, but they may have been either yellow or red. Some 

 were a deeper, more intense color than either F 2 parent. Female 2f 

 gave 13 F 3 young, of which 5 were cream and 8 were yellow. The 

 creams when born were absolutely white, and a microscopic examination 

 of their hair cleared in xylol and mounted in Canada balsam showed no 

 pigment. Later in life they acquired some yellow pigment in the medulla 

 of the hair but little or none in the cortex and gave the general appearance 

 of a very light straw-color. The presence of red, yellow, and cream 

 among the F 3 offspring from yellow parents suggested that yellow might 

 after all be an intermediate condition and that a lighter shade like cream 

 is recessive. We did not know at that time whether a single pair of 

 factors with incomplete dominance was involved or whether there were 

 a number of independent factor pairs for yellow, the cumulative effect 

 of which gave the more intense shades 



If a single alleomorphic pair with incomplete dominance were respon- 

 sible, then all the offspring from the F 3 creams should have been cream. 

 Three F 3 animals ( S 2f-a, 9 2f-b, 9 2f-e) classified as cream (white at 

 birth but very light straw-color when adults) were bred inter se to give the 

 F 4 generation. However, the offspring from these creams were not all 

 cream, for 9 2f-b produced 4 creams, but 9 2f-c gave 4 creams, 3 yellows, 

 and 1 red. This hypothesis, therefore, becomes untenable. The dif- 

 ference between the creams and yellows or reds in this last litter, as 

 in all others, was a distinct one, and there can be no question as to the 



