CHAPTER XIII 



CERTAIN COMPLICATIONS 



In the lijht of our present knowledge of heredity 

 the analysis of a plant or animal — the determination 

 of the factors upon which the various characters 

 depend — is often a simple process though it may 

 be a laborious one. Were any one fired with the 

 ambition of providing a complete factorial analysis 

 of all of the colours and shades that occur in the 

 flowers of the sweet-pea, he would probably encounter 

 few difficulties. Given an eye for shades of colour, 

 perseverance, and an elementary knowledge of the 

 principles of Mendelian heredity, he should be able 

 to furnish every form of flower with its appropriate 

 formula of factors within a reasonable time. But it 

 not infrequently happens that unexpected complica- 

 tions appear, obscuring an analysis pursued in the 

 orthodox way. A trained investigator to-day, start- 

 ing to explore the genetic constitution of a creature 

 by the methods of cross-breeding, would- in all 

 probability frame some working hypothesis at an 

 early stage in his experiments. The nature of an 

 F generation, the numbers and proportions of the 

 different forms in F.,, would at once suggest in- 



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