BOOTING. 



45 



smaller numbers and to other circumstances that will be discussed later, 

 the results are less regular in the Dark Brahma offspring, but in both the 

 range is from 2 or 3 upward to 10, with a great preponderance in grades 

 above 5. In the Silkies, on the other hand, the greatest frequency is found 

 in grades below 5. This difference is correlated with a difference of the 

 parents, for the commonest grades of the parents of the Cochins are between 

 6 and 10, of the Dark Brahmas between 5 and 9, and of the Silkies between 

 1 and 3. These results suggest that the Silkie is typically heterozygous 

 in boot, producing 25 per cent recessives (boot of grade 4-7) and 75 per cent 

 dominant (0, 1) and heterozygous (2, 3). We shall see that this hypothesis 

 receives support from all Silkie matings. 



Inside of any part of this table it appears that, on the whole, as the 

 average grade of the boot in the progeny diminishes that of the parentage 

 diminishes, although the correlation is by no means perfect. Thus the 

 average of the parental grades in the first part of table 31, A (which is 

 arranged in descending order of the averages of the offspring) is 8.5; in 

 the lower half, 7.4. The average of parental grades in the upper half of 

 table 31, B is 6.4; in the lower half 5.5. In table 31, C the grades are 2.9 and 

 2.3, respectively. This correlation indicates, without exactly measuring, 

 heredity in grade of booting. 



Table 32 shows the results of crosses between Cochins (high grade of 

 boot) and Silkies (low grade) . 



So far as the average grade of boot in offspring goes, this table stands 

 between that of the Cochins (table 31, A) and that of the Silkies (table 31, C). 

 But what is especially striking is the apparent dimorphism revealed in the 

 line of totals. There is one (empirical) mode at 10, corresponding with that 

 of the Cochins, and a second clear mode at 5, corresponding to that of the 

 Silkies. If we assume the Cochin to be homozygous in boot (RR) and the 

 Silkie to be heterozygous in boot, then we can interpret the high mode as 

 extracted recessives, the median mode as heterozygotes. 



