27 



Pearl ('09) reports a correlation coefficient of only .031 ±.072 between mothers 

 and daughters in hatchabihty, but only 87 indi\dduals were studied. Dunn ('23) 

 states that he was unable to separate high and low hatching Hnes by two genera- 

 tions of selection. He did find, however, that families tend to become different 

 in hatching power and to retain this difference. 



Table 5 clearly indicates that hatching power is transmitted from mother to 

 daughter, even though rigid control of the many environmental factors that modify 

 the hatching power is very difficult. These varying conditions often obscure the 

 true hatching ability of the pullet as an individual. The use of breeding females 

 of high hatching power is the first step toward improving the flock in this par- 

 ticular characteristic. We have shown in section 3 that the hatching power 

 of a pullet is sensibly correlated with her later hatching power. Follow this by 

 using breeding hens that transmit high hatchabihty to all of their daughters. The 

 male 's part in heredity of hatchabihty will next be considered. 



PART II. 

 The Male's Role in Inheritance op Fertility and Hatchability, 



Section 6. The Constancy of Fertility in Males. 



In studying the question of the inheritance of fertility and hatchability, much 

 importance should be attached to the male side of the flock, for the male is more 

 than half the flock from a genetic standpoint because each male furnishes half the 

 inheritance to the progeny of several hens. 



The measure of the male's fertilizing ability is the mean degree of fertility from 

 his dilTerent matings. The accuracy of such a measure ^vill of course depend upon 

 whether or not high fertility is governed in inheritance by dominant or recessive 

 factors, or whether it is independent of Mendelian factors. If high fertility depends 

 upon recessive factors, we should expect less variation in the daughters from a hen 

 that carries these factors pure, so that she herself is genetically highly fertile, than 

 would be the case if high fertility is dependent on dominant factors and these were 

 not in homozygous condition. The fact that manifestation of fertility in the eggs is 

 probably dependent on both male and female makes the classification of either 

 males or females with regard to this characteristic a hazardous undertaldng. A 

 careful analysis of the results from mating specific males to a number of females 

 in successive years with conditions kept uniform would help much to explain this 

 confusing problem. 



The problem of the constancy of a male's ability to transmit a certain degree of 

 fertility to his daughters may be elucidated by correlating the fertility of his 

 daughters sired during his first breeding year -uith that of his daughters sired during 

 the second breeding year, using pullet records in all cases. In other words, if males 

 transmit a certain degree of fertihty to their daughters in successive years, a posi- 

 tive correlation will exist. Such a tabulation is made from data available in table 

 6. Unfortunately, records on only 51 pairs of daughters are obtainable for study. 

 The number is small because few males are used as breeders after their cockerel 

 year. 



