312 LEROY POWERS 



were taken from the following publications: Powers and Lyon (1941), 

 Powers, Locke, and Garrett (1950), and Powers (1950a). The data will be 

 analyzed to obtain information concerning the recombination of the genes 

 differentiating weight per locule and number of days from seeding to first 

 fruit ripe. Also, the data will be studied to ascertain the probable bearing 

 this information has upon the production of inbred lines, by gene recombina- 

 tion, that retain some or all of the advantages attributable to heterosis of 

 yield of ripe fruit per plant which the hybrid populations would be expected 

 to exhibit. 



On the arithmetic scale the Danmark X Red Currant populations show 

 partial phenotypic dominance for smaller weight per locule. The parents of 

 the Danmark X Red Currant hybrid were found to be differentiated by a 

 large number of gene pairs (probably more than 40) which individually had 

 minor effects. From these results it is evident that, if somewhere near one- 

 half of the genes for smaller weight per locule in the Danmark X Red Cur- 

 rant hybrid populations had entered the cross from one parent and the 

 balance from the other parent, smaller weight per locule would have shown 

 heterosis. Some of the genes must be linked because the parents have a 

 haploid chromosome number of 12. In fact, since 40 or more pairs of genes 

 are differentiating the parents, it seems highly probable that a system of 

 linked polygenes is involved. With 40 pairs of genes differentiating the par- 

 ents in the F2, to recover an individual possessing all of the genes for in- 

 creased weight per locule (without linkage) would require a population of 

 lO^'* individuals. The size of such a population can be appreciated by con- 

 sidering the fact that 10" is 100 billion. The bearing this has upon the 

 feasibility of recovering from segregating populations inbred lines retaining 

 much of the advantage that might be exhibited by Fi hybrids is apparent. 



The Red Currant parent which possesses small weight per locule also 

 possesses earliness of maturity. Hence, some of the genes tending to increase 

 weight per locule are almost certain to be located on the same chromosomes 

 with a non-beneficial gene or genes tending to increase the time required for 

 maturity. However, due solely to the large number of gene pairs differentiat- 

 ing weight per locule, with no close linkage, pleiotropy, or unfavorable in- 

 terallelic and intraallelic interactions of the genes, only a comparatively 

 small amount of the increased weight per locule of the Danmark parent could 

 be combined with the earliness of maturity of the Red Currant parent by 

 selection in the F2 or backcross populations. 



Weight per locule and earliness of maturity have a material influence on 

 yield of ripe fruit per plant (Powers, 1945). In some crosses (see Tables 19.7 

 and 19.8) greater weight per locule is at least partially dominant. Since the 

 shorter period for days from seeding to first fruit ripe for the Danmark X 

 Red Currant cross shows heterosis (Table 19.8) the hybrid populations would 

 be expected to show heterosis for yield of ripe fruit per plant in crosses hav- 



