قراءة كتاب Inheritance of Characteristics in Domestic Fowl

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‏اللغة: English

Inheritance of Characteristics in Domestic Fowl

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المؤلف:

Davenport Charles Benedict

دار النشر: Project Gutenberg

الصفحة رقم: 2

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3. Silkie × Buff Cochin 76 4. White Leghorn × Black Minorca 77 5. White Leghorn × Buff Cochin 77 6. Black Cochin × Buff Cochin 78 Chapter XI. Inheritance of Blue Color, Spangling, and Barring 79 A. Blue Color 79 B. Spangling 80 C. Barring 81 1. White Cochin × Tosa 81 2. White Leghorn Bantam × Dark Brahma 82 3. White Leghorn Bantam × Black Cochin 82 Chapter XII. General Discussion 85 A. Relation of Heredity and Ontogeny 85 B. Dominance and Recessiveness 88 C. Potency 92 D. Reversion and the Factor Hypothesis 93 E. The Limits of Selection 94 1. Increasing the Red in the Dark Brahma × Minorca Cross 94 2. Production of a Buff Race by Selection 95 F. Non-inheritable Characters 96 G. The Rôle of Hybridization in Evolution 97 Literature Cited 99

INHERITANCE OF CHARACTERISTICS
IN DOMESTIC FOWL.

BY

CHARLES B. DAVENPORT.

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; but as the potency of dominance increases in the parents the proportion of offspring with the dominant (single) comb increases from 25 per cent to 50 per cent. This leads to the conclusion that, on the one hand, dominance varies quantitatively and, on the other, that the degree of dominance is inheritable.

The studies on polydactylism reveal a similar variation of potency in dominance and show, in Houdans at least, an inheritance of potency (table 11), and moreover they suggest a criticism of Castle's conclusion of inheritance of the degree of polydactylism.

Syndactylism illustrates another step in the series of decreasing potency of the dominant. On not one of the F₁ generation was the dominant (syndactyl) condition observed; and when these hybrids were mated together the dominant character appeared not in 75 per cent but in from 10 per cent to 0 per cent of the