264 



GENETICS AND PLANT BREEDING 



QUESTIONS 



1. What is the difference between sexual 

 reproduction and genetic transduc- 

 tion? 



2. Of what substances does DNA con- 



sist and why is an understanding of 

 DNA important to us? 



3. How does phage transduction seem 

 to operate? 



W. Gordon Whaley 



The Gifts of Hybridity 



Reprinted with the permission of the publisher 

 and author from The Scientific Monthly 70: 

 10-18, 1950. 



In the year 1932 com was planted 

 on 113,024,000 acres of United States 

 farm land. The total yield for that year 

 was 2,930,352,000 bushels, an average 

 of 25.9 bushels per acre. In the year 

 1946, 3,287,927,000 bushels were har- 

 vested from plantings on 90,027,000 

 acres, representing a per acre yield of 

 36.5 bushels. The difference in vield 

 was due in greatest measure to the use 

 of hybrid corn on a large scale. The 

 production of 36 bushels to the acre 

 instead of 26 represents nothing short 

 of a revolution. The importance of the 

 revolution extends even further than 

 the increased yield figures indicate, for 

 it has freed approximately 23,000,000 

 acres of land for the growing of other 



crops or for inclusion in a hedge against 

 soil fertility exhaustion. 



These developments suggest star- 

 tling potentialities for other crops, and 

 they may be a consideration pointing 

 the way out of the dilemma of increas- 

 ing populations and decreasingly fertile 

 farm lands with which most of the 

 Temperate Zone countries of the world 

 are faced. 



The superiority of hybrid com has 

 its basis in a little-understood phe- 

 nomenon known to biologists as hetero- 

 sis. Whatever mav be involved, hetero- 

 sis gives to hybrids a developmental 

 vigor which makes them larger, higher- 

 yielding, improves the quality of their 

 products, or othenvise renders them 



