Independent Recombination by Nonalleles 53 



William Bateson (1861-1926). 



(From Genetics, vol. 12, 



p. 1, 1927.) 



basis for the independent recombination of such nonalleles is that different pairs of 

 genes reside in nonhomologous pairs of chromosomes. 



The phenotypic expression of genes depends upon their alleles, insofar as dominance 

 is involved, and upon nonalleles, insofar as epistasis (including superposition, coopera- 

 tion, and antagonism) and the production of apparently novel phcnotypes are involved. 

 The absence both of dominance and of epistasis will always produce phenotypic ratios 

 which directly represent genotypic ratios, whereas the occurrence of one, the other, 

 or both reduces the number of phenotypic classes. In any case, segregation and inde- 

 pendent segregation, being genetic properties, are totally uninfluenced by the manner 

 whereby genes do or do not come to phenotypic expression. 



REFERENCES 



Bateson, W., Mendel's Principles of Heredity, Cambridge, England: Cambridge Uni- 

 versity Press, 1909. 



Mendel, G. See reference at the end of Chapter 3. 



Supplement I (at the end of this book). 



QUESTIONS FOR DISCUSSION 



4.1. Make genetic diagrams for the crosses and progeny discussed in the second and 

 third paragraphs on p. 42. Be sure to define your symbols. 



4.2. Is a test cross or backcross used to determine genotypes from phenotypes in cases 

 of no dominance? Explain. 



