INHERITANCE OF EGG CHARACTERS 17 



Small-egg Large-egg 



Line A 



Line B . . . . 



Line C 



These studies indicate that a gene C for large egg size exists and is responsible 

 for eggs that weigh 63 grams (26.7 ounces to the dozen) or more, laid by 

 pullets when about eleven months old. These data further confirm previous 

 findings that a gene A for small eggs occurs and that gene B for medium egg 

 weight also operates. The data point further to a third gene C for large eggs 

 and indicate that gene A is epistatic to both B and C. The general status of 

 egg weight inheritance may be summarized: 



Gene A alone gives small egg size. 



Genes A and B together give a hatching-season egg weight below 57 grams 



or small. 

 Gene B alone gives medium egg weight 57 to 62.9 grams. 

 Gene C alone probably gives medium also. 

 Gene C with B gives large egg size. 

 Gene C with A gives medium. 

 Gene C with A and B gives medium. 



Fixing Large Egg Size in the Flock 



In a flock that has been bred for high fecundity there may be wide variability 

 in egg weight. Uniformly large eggs produced in large numbers are very de- 

 sirable. When mean egg size is lower than desired it is an indication of the 

 presence of gene A in a considerable number of the population. Selective 

 breeding from parents of the medium or large phenotypes is effective in increas- 

 ing egg size because gene A is lacking. The use for breeding of males and 

 females of the large phenotype is not more effective in raising the mean egg 

 size of the daughters than the use of breeders of the medium type because the 

 chances of bringing genes B and C together are fewer than the chances of 

 producing birds carrying either genes B or C alone. It is probable that birds 

 carrying gene C alone fall into the medium phenotype in egg size and the large 

 egg type appears to arise from the cumulative action of genes B and C. 



Economically, extreme egg weight is not desirable. In the first place ex- 

 tremely large eggs do not hatch as well as eggs of medium size. In the second 

 place, very large eggs are likely to have poorer shells. In the third place, large 

 eggs produce more reproductive injuries. In the fourth place the market does 

 not ordinarily pay a premium for very large eggs that are produced at greater 

 expense. In view of these facts a maximum egg weight for the pullet year 

 should be about 61 grams or 26 ounces to the dozen and for later years about 

 65 grams or 27.5 ounces to the dozen. 



