INDIRECT EVIDENCE FROM DUPLEX HYBRIDS 

 BEARING UPON THE NUMBER AND DIS- 

 TRIBUTION OF GROWTH FACTORS 

 IN THE CHROMOSOMES 



DE. D. F. JOXES 

 Connecticut Agricultural Experiment Station, I^ew Haven 



Sufficient evidence lias accumulated to indicate tliat 

 the main features of the chromosome theory of hereditary 

 transmission, as worked out for Drosophila, are appli- 

 cable, to plants. Peas, primula and maize have been the 

 best materials so far to demonstrate linkage of factors in 

 plants. Owing to the ease of culture, large number of 

 seeds produced and the great genetic variability the 

 maize plant is becoming very useful in this line of in- 

 vestigation. The agricultural importance of the plant 

 and the large number of people working with it have al- 

 ready made the list of Mendelian factors definitely de- 

 termined large and increasing rapidly. Due mainly to 

 the industry of Professor Emerson and his co-workers 

 at Cornell University, six linked groups are already 

 visible in rough outline, some of which have a goodly 

 number of factors fairly well located. It therefore seems 

 pertinent to consider some indirect evidence funished 

 by this plant having a bearing upon the chromosome 

 mechanism. 



In working out the best means of utilizing inbred 

 strains of corn for the purpose of increasing production 

 it has been found to be advantageous to cross again two 

 different first generation hybrids each of which were the 

 result of combining two different self -fertilized families. 

 Altogether four homozygous types, each differing from 

 the other in many visible characters, are brought together 

 in this way in a progeny which has an extremely complex 

 composition. Assuming that the inbred strains have been 

 reduced to complete homozygosity, the first generation 

 hybrid is uniform. Statistical measurements show this 

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