72 



The Journal of Heredity 



The average mathematical possibih- 

 ties of segregation from all possible 

 mating combinations are given in Table 

 III. 



Apparent Contradictions Explained 



Apparent contradictions are not so 

 great as would seem at first glance ; a 

 comparison of theoretical possibilities 

 with actual recorded results are given 

 in Table III. It is obvious that the 

 greatest source of error is the registra- 

 tion of red individuals. The recording 

 or twelve per cent red-and-white, three 

 Y>eY cent roan and one per cent white 

 from this mating is sufficiently close to 

 the theoretical possibilities to be within 

 the limits of probable error. One or 

 both the parents in these cases must 

 have been genotypically red-and-white. 

 but the pattern in the phenotype showed 

 so great a preponderance of red that 

 the individual was recorded as a red 

 ( see Figure 5 ) . 



The appearance of such individuals 

 as Rosczvood Radium, which shows a 

 phenotype carrying both roan and pied 

 pattern, can be explained by assuming 

 they have a genetic makeup of (RrEe), 

 with respect to the colors in question. 

 A true roan of the genetic form 

 ( RrEE ) is shown in Figure 4. On 

 this hypothesis if mated to (RrEE) 

 he would sire no true red-and-whites 

 of the formula (Rree). 



Theoretically a true red-and-white 

 (Rree) such as is shown in Figure 7, 

 crossed on (Rree) cows will produce 

 no roans. Actually between five and 

 ten per cent roans are recorded as re- 

 sulting from matings of red-and-white 

 on red-and-white. This is possible, 

 when it is considered that animals hav- 

 ing the zygotic formula (RrEe) may be 

 recorded as red-and-white. Matings of 

 (RrEe) and (Rree) would allow theo- 

 retical possibilities of twenty-five per 

 cent roans. In figuring the percentages 

 in Table 11 no allowance could be 

 made for this probable source of error, 



"RrEe is usually recorded as roan, as the American Short-Horn .\ssociation rules that 

 an individual may be recorded as a roan if roaning appears on any part of the body. How- 

 ever, no doubt many RrEe individuals are recorded as red-and-white. 



unquestionably proven by the results 

 obtained from the various matings in 

 Table III. The question logically 

 arises, why will a cross between red 

 and black produce no roans? The 

 reason is apparent when it is considered 

 that red and black are genetically, as 

 well as practically, true allelomorphs, 

 resulting in complete dominance of 

 black in the heterozygote. Which in 

 turn will separate out in the second 

 generation in the definite Mendelian 

 ratio of three dominants to one reces- 

 sive. This has been proven too often 

 to need further discussion. It will 

 serve, though, to show that the red of 

 the Short-Horn may be often associated 

 with the roan extension factor (E). 

 but its presence will not be proved as 

 it will not be brought to light in the 

 phenotype. 



Many of the apparent contradictions 

 which occur in the various color mat- 

 ings of Short-Horns can be eliminated 

 if it is assumed that red-and-white in 

 the Short-Horn is not caused by the 

 introduction of an extension factor en- 

 tirely different from roan (E), but is 

 really produced by the total absence of 

 E and can be represented as (e). When 

 this occurs in the presence of a hete- 

 rozygous condition for red ( R ) a red- 

 and-white animal is produced. 



A logical basis has now been estab- 

 lished for assuming genetic formulae 

 for the various phenotypes, viz : 



Red=r 



Roan^ 



White: 



RRee 



RREE 



RREe 



RrEE 



RrEe' 



rrEE 



rrEe 



rree 



Red-and-White= -l Rree 



