308 



LEROY POWERS 



more than one class are greater than 19: 1. When interpreting the data it is 

 necessary to have in mind that parental percentage values would have fallen 

 into the complete dominance columns, the Pi value into the first such col- 

 umn, and the Pi into the second such column. Also, it should be kept in mind 

 that the values listed in Table 19.7 are for the different Fi hybrids, and with 

 the exception of the values listed under the columns headed "heterosis" are 

 percentages based on the means of the two respective parents. The percent- 

 ages listed under the heterosis columns are based on the mean of the parent 

 that fell into the adjacent complete dominance columns. 



TABLE 19.7 



PERCENTAGE RANGE IN EXPRESSION OF DOMINANCE FOR 

 DIFFERENT CHARACTERS OF Fi TOMATO HYBRIDS* 



* As measured by percentages of averages of values of parents and percentages of parental values. 



If dominance and heterosis are different degrees of expression of the same 

 physiological genetic phenomena, then the different genotypes, as represented 

 by the different Fi hybrids, might be expected to show ranges in expression 

 of a given character from different degrees of dominance to heterosis. 



Every character listed in Table 19.7 except number of days from first fruit 

 set to first fruit ripe, in the different hybrids, ranges from some degree of 

 dominance to heterosis. Yield in grams of ripe fruit per plant, depending 

 upon the genotype (Fi hybrid), varied from no dominance through all classes 

 to heterosis for increased yield. Number of ripe fruit per plant and height of 

 plant varied through all classes from partial dominance of a decrease in mag- 

 nitude of these two characters to heterosis for an increase. Weight of fruit 

 in grams, number of days from seeding to first bloom, and number of locules 

 per fruit varied from no dominance to heterosis for a decrease of these char- 

 acters. Considering all of the characters there is a continuous array of values 



