Dunn, Schneider and Webb: Spotting in Cattle 



237 



heritance is in g'eneral a matter of in- 

 dividual differences and separable 

 traits. We may, however, conclude 

 that the average result of crossing 

 animals of different grades is the pro- 

 duction of offspring whose overage 

 grade is intermediate between those of 

 the parents. This is purely a statement 

 of average facts and not an explana- 

 tion of the inheritance. 



We next attempted to determine the 

 differences in the hereditary contribu- 

 tions of the different sires used by 

 measuring the resemblance or correla- 

 tion in spotting between individual 

 calves and their dams for each prog- 

 eny group separately. We reasoned 

 that if the germ cells of the sire con- 

 tained factors recessive to those of the 

 dams then there should be a high de- 

 gree of resemblance between dam and 

 offspring, because the contribution of 

 the sire should not be visible in his 

 offspring. If, on the other hand, the 

 sire contributed dominant factors, the 

 resemblance between offspring and 

 dams should be altered (correlation 

 lowered) by the "interference" of the 

 factors from the male. If there were 

 no dominance, the contributions of sire 

 and dam to the offspring should be of 

 equal effect and variation in the dams 

 should be accompanied to some ex- 

 tent by variation in the offspring, re- 

 sulting in low correlation between 

 dams and offspring. This reasoning 

 we believe to be sound, but in our own 

 case many practical difficulties stand 

 in the way of a direct application of 

 this method. Chief of these is the fact 

 that for at least two of the sires used 

 we cannot be certain that the germ 

 cells produced are alike ; we have no 

 good evidence that they are homo- 

 zygous. Another difficulty is the fact 

 that all three sires were not bred to 

 exactly the same types of cows. The 

 cows to which the light and dark bulls 

 were bred are roughly of similar dark- 

 ness, but the cows to which the me- 

 dium bull was bred were darker than 

 the other two groups. The most 

 profitable procedure is therefore to 

 compare the degree of dam-offspring 



resemblance in the progenies of the 

 light and the dark sires. 



The dam-offspring correlations are 

 given in the last column of Table 1. 

 There proved to be a high correlation 

 (r = -|- .61) between the dams and off- 

 spring of the light bull (King Model) 

 indicating that the factors contributed 

 by this male were probably recessive 

 to those of the dam. If the coat pat- 

 terns of the offspring were determined 

 wholly by the heredity of the sire and 

 dam, then the contribution of the light 

 sire has much less visible effect on the 

 coat character of the offspring than 

 the contribution of the darker dams. 

 This last assumption is, however, 

 probably not justified since some non- 

 heritable variation exists. 



The correlation between dams and 

 offspring of the dark bull, while un- 

 doubtedly significant, is only about 

 half as great (r = -I- .34) as the corre- 

 lation between dams and offspring of 

 the light bull. The relative importance 

 of dam and sire is here reversed, the 

 dark male having the greater determin- 

 ative effect, indicating dominance of the 

 factors contributed by him. 



There proved to be no correlation 

 between the dams and the offspring of 

 the medium bull indicating possibly 

 equal determinative effect of the con- 

 tributions of sire and dam. Because 

 of the probable independent segrega- 

 tion of spotting factors taking place in 

 this cross (see below) indicating a 

 heterozygous genotype for the male 

 and many of the females in these mat- 

 ings, and because of the difference in 

 mean grade of the mated cows we pre- 

 fer to draw no conclusions from this 

 correlation. 



Accepting this as partial evidence of 

 the dominance of the darker over the 

 lighter grades of spotting, we next at- 

 tempted to determine whether there 

 was any clear evidence of the segrega- 

 tion of factors aft'ecting the amount of 

 spotting. We divided all animals used 

 into three groups, classifying as 

 "light" those with from to 249 units 

 of "black; as "dark" those with 700 to 

 949 units of black ; and as "medium" 



