CHAPTER VIII. 



CREST. 



In my report of 1906 I called attention to the nature of inheritance 

 of the crest in the first and second generations. The result seemed simple 

 enough on the assumption of imperfect dominance. However, in later 

 generations difficulties appeared, one of which was referred to in a lecture 

 given before the Washington Academy of Sciences in 1907. I stated (1907, 

 p. 182), that "when a crested bird is crossed with a plain-headed one, and 

 the crested hybrids are then crossed inter se, the extracted recessives of the 

 second hybrid generation are plain-headed, to be sure, but they show a 

 disturbance of certain feathers." This was an illustration of the statement 

 that recessives which are supposed to come from two pure recessive gametes 

 show in their soma traces of the dominant type. Dr. W. J. Spillman, who 

 was present, made the suggestion that the crest is composed of two char- 

 acters, T and t, instead of a simple element, and that when t alone is present 

 the result will be the roughened short feathers on top of the head. 



Further studies demonstrate the validity of this suggestion. There are in 

 the crest two and probably three or more factors. There is a factor that deter- 

 mines length of the feathers and a factor that determines their erectness. 

 There is probably also an extension factor that controls the area that the 

 crest occupies on the head. Thus flatness of position dominates over its 

 absence (or erectness). This is seen even in the first generation. Figs. 5, 

 6, 8, and 17 of my report of 1906 show this very plainly. They also show 

 that continued growth of feather is dominant over interrupted growth. 

 Thus in the second hj^brid generation I got birds with short and erect feathers 

 and one of these is shown in fig. 11 of the 1906 report. That shortness is 

 recessive is proved by various matings of extracted short X short crest. 

 Of 29 offspring none have a higher grade than 1, grade 10 being of full 

 length. On the other hand, two parents with long feathers in the crest 

 (grades 6 to 8) give 5 offspring of grade 1, 12 of grades 5 to 10, thus approach- 

 ing the 1 : 3 ratio expected from two DR parents. That erectness is reces- 

 sive is proved by various matings of extracted erect X erect crest. Of 25 

 offspring none has a lower grade than 4 (1 case) or 5 (1 case). On the other 

 hand, two parents with extracted non-erect feathers give in 46 offspring 

 13 with feathers whose grade of erectness is 6 or higher and 33 with a grade 

 of 5 or below of these half of grade close to the expected 1:3. The 

 evidence is conclusive that there are two factors in crest that behave in Men- 

 deUan fashion a factor determining the prolonged growth of the feather 

 and a factor causing the feathers to lie repent. 



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