482 



JOHN W. GOWEN 



EFFECT OF THE GENOME COMPONENTS ON HYBRID VIGOR 



The combining capacity of a genome may be analyzed into its components 

 — the individual chromosomes. To make this analysis, Dr. Straus in our genet- 

 ics laboratory carried through duplicated experiments based on the cross of 

 Inbred 92 and Ames I. This cross, as noted previously, showed high hybrid 

 vigor. The following data were taken from his thesis (1942). 



The results showed no cytoplasmic effects. Effects of reciprocal crosses 

 also were found negligible. 



The first step in these investigations required that 8 possible homozygous 

 lines be created for the first, second, and third chromosomes. About 98.5 per 

 cent of the genes would be homozygous in each of the eight types. Crosses 

 of the eight different homozygous lines will give all the other types ranging 

 from those heterozygous in one chromosome pair to those heterozygous for 

 each chromosome. The productivities of these 27 different types together 

 with their chromosomal constitution are as follows: 



Heterozygous for 3 chromosome pairs 

 Heterozygous for 2 chromosome pairs 

 6 chromosome combinations 



Heterozygous for 1 chromosome pair 

 12 chromosome types 



Homozygous 

 8 types 



The analysis of the variance of the 1440 daily egg productions in this com- 

 pletely balanced factorial experiment shows that the difference between 

 chromosome effects makes the most important contribution to variation. 



From type 20 to 27, all types are homozygous or are of zero heterozygosity. 

 Types 8 to 19 have one chromosome heterozygous. Since each chromosome 



