LEROY POWERS 



USDA, Bureau of Plant Industry 



Chapter 19 



Gene Recombinotion 

 and Heterosis 



This article will be confined primarily to the tomato {Lycopersicon) genetic 

 work which has a bearing on gene recombination and heterosis. The barley 

 (Hordeum) genetic research which is discussed briefly was conducted at the 

 University of Minnesota. The tomato genetic research which constitutes the 

 bulk of the material discussed was conducted at the United States Horticul- 

 tural Field Station, Cheyenne, Wyoming. 



With the present available methods of analysis it is difficult in quantita- 

 tive inheritance studies to distinguish between blocks of fairly closely linked 

 genes and individual pairs of genes. This has been shown by the work of 

 Jones (1917), Warren (1924), Mather (1942, 1949), and Straus and Gowen 

 (1943). Consequently, in this article where the two genetic systems are not 

 distinguishable the term pairs of genes will be employed. Mather (1949) has 

 used the term ejffedive factor to depict such a genetic situation. 



MARKER GENES AND LINKAGE IN BARLEY 



Powers (1936) has shown that in a cross between Bl {Hordeum deficieiis) 

 and Brachytic {Hordeum vulgare) the Fi, which is a two-row barley, gave a 

 greater yield of seed per plant than either the two-row or six-row parents. 

 Then, weight of seed per plant shows heterosis. The data on marker genes 

 and linkage in barley presented have some bearing upon whether any of the 

 advantages of the Fi hybrid attributable to heterosis can be recovered in 

 inbred lines through gene recombinations. 



The deficiens (two-row) character was found to be differentiated from the 

 vulgare (six-row) character by one pair of genes designated as Vv, and the 

 brachytic character from the normal character by one pair of genes designated 



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