COMPOUND ALLELOMORPHS 353 



is technically called a simple allelomorph. But there are other 

 differentiating characters which seem to consist of several 

 components capable &i being isolated and of entering into new 

 combinations. These are called compound allelomorphs. 



Thus, to take Mr. Punnett's example, the " walnut " comb 

 of Malay fowls — broad, flattened, corrugated like half a walnut, 

 and with small bristle-like feathers posteriorly — becomes, as it 

 were, a compound allelomorph. " This is shown by the fact 

 that it may be synthesised from pure rose and pure pea. It 

 behaves as a dominant to rose, pea, and single * combs. In 

 a zygote formed by the union of walnut with rose or pea the 

 walnut character is stable, and such heterozygotes form an equal 

 number of gametes bearing the walnut, and either the rose or 

 the pea allelomorphs. In other words, the compound allelo- 

 morph is stable in the presence of certain presumed simple 

 allelomorphs. When, however, the zygote is formed by the 

 union of walnut with single, the compound allelomorph would 

 appear to undergo partial disintegration with the formation of 

 walnut, rose, pea, and single allelomorphs in equal proportions. 

 The zygote formed by the union of walnut with single is, so far 

 as we at present know, precisely similar to that produced by 

 the meeting of rose and pea " (Punnett, 1905, p. 40). 



Sometimes pairs of characters go inextricably together, so 

 that the breeder has not as yet been able to break their correla- 

 tion. Thus, violet colour and hairiness in Leucoja go together, 

 and so do whiteness and baldness in the same flower. 



Some very difficult cases are known where the inbred hybrids 

 have progeny some of which resemble one or both of the original 

 parent types, while others resemble quite different types. Thus the 

 Stanley variety of Lathynis odoralus, crossed with the Giant White 



* A high serrated " single " comb is familiar in Leghorns, etc. ; a flattened 

 papillated " rose " comb with a posterior pike is seen in Wyandottes, etc. ; 

 a low " pea " comb, with three well-marked ridges, the median slightly- 

 higher than the other two, is characteristic of Indian game-fowl. 



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