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INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL.
INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL.
BY CHARLES B. DAVENPORT, Director of the Station for Experimental Evolution, Carnegie Institution of Washington. WASHINGTON, D. C. Published by the Carnegie Institution of Washington. 1909 [ii] Carnegie Institution of Washington Publication No. 121. Papers of the Station for Experimental Evolution, No. 14. PRESS OF J. B. LIPPINCOTT COMPANY PHILADELPHIA...
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INTRODUCTION.
INTRODUCTION.
A series of studies is here presented bearing on the question of dominance and its varying potency. Of these studies, that on the Y comb presents a case where relative dominance varies from perfection to entire absence, and through all intermediate grades, the average condition being a 70 per cent dominance of the median element. When dominance is relatively weak or of only intermediate grade the second generation of hybrids contains extracted pure dominants in the expected proportions of 1:2:1;
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A. INTERPRETATION OF THE Y COMB.
A. INTERPRETATION OF THE Y COMB.
When a bird with a single comb, which may be conveniently symbolized as I , is crossed with a bird with a "V" comb such as is seen in the Polish race, and may be symbolized as oo , the product is a split or Y comb. This Y comb is a new form . As we do not expect new forms to appear in hybridization, the question arises, How is this Y comb to be interpreted? Three interpretations seem possible. According to one, the antagonistic characters (allelomorphs) are I comb and oo comb, and in the product
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B. VARIABILITY OF THE Y COMB AND INHERITANCE OF THE VARIATIONS.
B. VARIABILITY OF THE Y COMB AND INHERITANCE OF THE VARIATIONS.
As already stated, the proportions of the median and the lateral elements in the Y comb are very variable; the median element may, indeed, constitute anywhere from 100 per cent to 0 per cent of the entire comb. Even full brothers and sisters show this variability. Thus the offspring of No. 13 ♀ Single-comb Minorca and No. 3 ♂ Polish have the median element of the Y comb ranging from 0 per cent to 70 per cent of the whole comb. Notwithstanding this variability of the median element in any family
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A. TYPES OF POLYDACTYLISM.
A. TYPES OF POLYDACTYLISM.
There are two main types of polydactylism: that in which the inner toe (I) of the normal foot is replaced by 2 simple toes, and that in which it is replaced by two toes, of which the mediad is simple and the laterad is divided distally. The former type is characteristic of the Houdans; the latter is usually associated with the Silkies. Both conditions are, however, found in both races. The simplest condition is seen in many Houdans of my strain. It consists of 2 equal, medium-sized toes (I' and
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B. RESULTS OF HYBRIDIZATION.
B. RESULTS OF HYBRIDIZATION.
First let us consider the result of mating extra-toed individuals belonging to "pure" extra-toed races. A typical Houdan cock (D type), of the well-known Petersen strain, was mated with 3 hens bred by me, but derived, several generations before, from the same strain. With the first hen he got 29 chicks, all with the extra-toe except one (3.3 per cent) that had 4 toes on both feet and two that had 4 toes on one foot and 5 on the other, i. e. , one foot simplex and one duplex. With the second he g
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A. STATEMENT OF PROBLEM.
A. STATEMENT OF PROBLEM.
In man, various mammals, and some birds two or more adjacent fingers are sometimes intimately connected by an extension of the web that is normally a mere rudiment at their base. Such a condition is known as syndactylism. A good introductory account of syndactylism is given by Bateson (1904, pp. 356-358). Taking a number of cases of syndactylism together, he says: "A progressive series may be arranged showing every condition, beginning from an imperfect webbing together of the proximal phalanges
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B. RESULTS OF HYBRIDIZATION.
B. RESULTS OF HYBRIDIZATION.
In taking up the results of breeding experiments to test the method of inheritance of syndactylism, it will be best first to give in a table all pens in which the character showed itself, with the frequency of the different types of foot in them (table 23). The history of the syndactyl strain begins with No. 121 ♀ and in the matings 1 to 8 are given the results of crossing together some of her progeny derived from a normal-toed father. This father was either No. 8 a or 1 a , both full-blooded To
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CHAPTER IV. RUMPLESSNESS.
CHAPTER IV. RUMPLESSNESS.
The tail of vertebrates is, historically, the post-anal part of the trunk. Containing no longer any part of the alimentary canal, it has lost much of its primitive importance, so that its disappearance in any case is a matter of relatively little importance. Accordingly we find groups of animals in which it is rudimentary or wholly absent, such as many amphibia and the anthropoid apes and man. In all recent birds the tail is a distinct but much reduced organ—the uropygium—which contains several
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CHAPTER V. WINGLESSNESS.
CHAPTER V. WINGLESSNESS.
The entire absence of appendages is a rare monstrosity, few cases having been cited even for man. In my experience with poultry, out of about 14,000 birds I have obtained one that had no wing on one side of the body, but this unfortunately died before being bred from. A second bird was given to me by a fancier. The bird was an Indian Game, a vigorous cock, which was handicapped by his abnormality in two ways. First, whenever he fell upon his side or back he was unable to get upon his feet withou
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A. TYPES OF BOOTING.
A. TYPES OF BOOTING.
The races of booted poultry used have been as follows: First, bantam Cochins of two varieties; second, a bantam Dark Brahma; and third, the Silkie. In my representatives of the first two groups, but particularly in the Dark Brahma, the amount of booting is variable. In one type the outer third of the shank in the newly hatched chick is covered by strong, heavy, specialized feathers, directed outward, while the middle and inner thirds are covered by smaller, finer, imbricating feathers sparsely p
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B. NORMAL VARIABILITY.
B. NORMAL VARIABILITY.
To appreciate the results of hybridizing we must first examine the variability of pure-blooded races. This is done in table 31. Table 31. — Distribution of boot-grades in the offspring of Cochin, Dark Brahma, and Silkie parents. An inspection of table 31 shows that, in respect to booting, the Cochins and Dark Brahmas are clearly closely related to each other. Owing to smaller numbers and to other circumstances that will be discussed later, the results are less regular in the Dark Brahma offsprin
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C. RESULTS OF HYBRIDIZATION.
C. RESULTS OF HYBRIDIZATION.
We have next to consider the nature of the inheritance when one parent belongs to an unbooted race, the other to a booted one (table 33). Table 33. — Distribution of boot-grades in the F 1 generation of booted × non-booted parents. An inspection of Table 33, which gives the distribution of grades of boot in the offspring constituting the first hybrid generation, might well lead to the conclusion that inheritance is here of a blending nature, or that, if either condition is dominant, it is the bo
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CHAPTER VII. NOSTRIL-FORM.
CHAPTER VII. NOSTRIL-FORM.
In my 1906 report I described in detail the form of the nostril in poultry. Usually it is closed down to a narrow slit, but in some races, as, e. g. , the Polish and Houdans, the closing flap of skin fails to develop and the nostril remains wide open. This is apparently an embryonic condition. Thus in Keibel and Abraham's (1900) Normaltafeln of the fowl it is stated that the outer nasal opening, which is at first wide open, becomes closed with epithelium at about the middle of the sixth day of d
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CHAPTER VIII. CREST.
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 re
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CHAPTER IX. COMB-LOP.
CHAPTER IX. COMB-LOP.
In races having a large single comb this is usually erect in the male, but in the female lops over to the right or left side of the head. This lop is determined before hatching; indeed, in the male it may be ascertainable only in the embryo or in the recently hatched chick. The position of the comb is permanent throughout the life of the pullet and hen and, if pressed to the opposite side, it quickly returns to its original position. At one time I entertained the hypothesis that its position was
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A. THE GAMETIC COMPOSITION OF THE VARIOUS RACES.
A. THE GAMETIC COMPOSITION OF THE VARIOUS RACES.
Plumage color, like hair color, varies greatly among domesticated animals. This diversity is, no doubt, in part due to the striking nature of color variations, but chiefly to the fact that the requisite variations are afforded in abundance. The principal color varieties, in poultry as in other domesticated animals, are melanism, xanthism, and albinism. In addition, poultry show the dominant white, or "gray" white, first recognized in poultry by Bateson and Saunders (1902), which is also found in
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B. EVIDENCE.
B. EVIDENCE.
The evidence for the gametic interpretations of the self-colored fowl is derived from hybridizations. It will now be presented in detail. By hypothesis this cross is between cJnwx and CJNwx . The first generation should give the zygotic formula CcJ 2 Nnw 2 x 2 , or, more simply, CcJ 2 Nn . This formula resembles closely that for the Minorca; but it differs in this important respect, that the coloring factor and the supermelanic factor are both heterozygous, and hence diluted. Actually I found, a
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A. BLUE COLOR.
A. BLUE COLOR.
Color-patterns are generalized, like the barring, spangling, and "blueing"; or localized, like the wing-bar or hackle and saddle lacing. We have to consider at present the method of inheritance of the former of these kinds of color patterns. As is well known (Bateson, Saunders, and Punnett, 1902, 1903), the Blue or Andalusian fowl is a heterozygote and, as such, produces white gametes and also black gametes. [10] The "blue" is, indeed, a fine mosaic of white and black. The barbules of a blue fea
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B. SPANGLING.
B. SPANGLING.
As is well known, hybrids between black fowl and White Leghorns are usually white with black patches in the females, while their brothers are mostly entirely white. This "spangled" condition is a heterozygous one just as truly as the "blue" condition is. When a splashed hen is mated to her white brother a certain proportion of the offspring are splashed again, i. e. , one-half of 50 per cent or 25 per cent, that being the proportion of heterozygous females. Actually in 150 offspring 19.4 per cen
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C. BARRING.
C. BARRING.
The presence of bands of black running at intervals across the otherwise white feather is a condition found in many types of poultry as well as various wild birds. It has become a fixed character in the Barred Plymouth Rock, which derived it in turn from the barred Dominique, whose barring was probably derived from the Cuckoo birds of England. Barring is also said to result from some crosses between white and black birds. In my breedings barred birds have arisen several times: (1) White Cochin ×
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A. RELATION OF HEREDITY AND ONTOGENY.
A. RELATION OF HEREDITY AND ONTOGENY.
In studying heredity our attention must often be focused on the ontogenesis of the different characters, and we are sometimes inclined to regard the adult character as the product of the course of ontogenesis. But this is a superficial way of looking at things; the determiners of all characters are in the germ-plasm and together they direct the development of one part after another in orderly succession; a modernized form of the pre-formation doctrine seems logically necessary. What do we know o
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B. DOMINANCE AND RECESSIVENESS.
B. DOMINANCE AND RECESSIVENESS.
If segregation is the cornerstone of modern studies in heredity, dominance forms an important part, at least, of the foundation. In any case, a critical examination of dominance is now required; the more so since its significance and value have often been doubted. First, how is a dominant character to be defined? It has been defined both on the basis of visible results in mating and on the basis of its essential nature. On the basis of visible results in hybridizing dominant characters may be de
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C. POTENCY.
C. POTENCY.
Perhaps an apology is needed for introducing the much-abused word "potency"; but there is hardly another that can be so readily adapted to the precise definition I desire to give to it. The potency of a character may be defined as the capacity of its germinal determiner to complete its entire ontogeny. If we think of every character as being represented in the germ by a determiner, then we must recognize the fact that this determiner may sometimes develop fully, sometimes imperfectly, and someti
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D. REVERSION AND THE FACTOR HYPOTHESIS.
D. REVERSION AND THE FACTOR HYPOTHESIS.
The brilliant development of the factor hypothesis, only dimly fore-shadowed by Mendel [17] (1866, p. 38), clearly expressed by Correns (1892), applied to animals by Cuénot, and further elaborated by Bateson and Castle and their pupils, has quite changed the methods of work in heredity. More forcibly than ever is it brought home to us that the constitution of the germ-plasm—not merely the somatic character—is the object of our investigation. With this principle fully grasped the existence of cry
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E. THE LIMITS OF SELECTION.
E. THE LIMITS OF SELECTION.
In the last few decades the view has been widespread that characters can be built up from perhaps nothing at all by selecting in each generation the merely quantitative variation that goes farthest in the desired direction. I have made two tests of this view, using the plumage color of poultry. (1) Increasing the red in the Dark Brahma × Minorca cross. —The Dark Brahma [19] belongs to the group of poultry that contains a majority of characters derived from the Aseel type. Nevertheless, its pluma
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F. NON-INHERITABLE CHARACTERS.
F. NON-INHERITABLE CHARACTERS.
So well-nigh universal is heredity that it is justifiable to entertain a doubt whether any character may fail of inheritance. So far as my experience goes, non-inheritable characters are such as are weak in ontogeny, so that they may readily fail of development even when conditions are propitious; or else they are so complex—so far removed from simple unit-characters—that their heritability in accordance with established canons is obscured. The first case is apparently illustrated by the rumples
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G. THE RÔLE OF HYBRIDIZATION IN EVOLUTION.
G. THE RÔLE OF HYBRIDIZATION IN EVOLUTION.
The criticism has often been made of modern studies in hybridization that they are really unimportant for evolution because hybridization is uncommon in nature. Even at the beginning of the new era it could be replied that, first, we did not know how common hybridization might turn out to be in nature, and, second, that certainly in human marriage and among domesticated animals and plants, intermixing of characters played a most important part, and, finally, the laws of inheritance of characters
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LITERATURE CITED.
LITERATURE CITED.
Baldamus, A. C. E. 1896. Illustrirtes Handbuch der Federviehzucht. Erster Band: Die Hühnervogel. 3 Aufl. bearbeitet von O. Grünhaldt. Dresden, 1896. xvi+476 pp., 102 figs. Barfurth, D. 1908. Experimentelle Untersuchung über die Vererbung der Hyperdactylie bei Hühnern. I. Mitth. Der Einfluss der Mutter. Arch. f. Entw.-Mech. der Org., XXVI , 631-650. Bateson, W. 1894. Material for the Study of Variation Treated with Especial Regard to Discontinuity in the Origin of Species. London, 1894, xvi+598 p
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