Apr. 19,1924 Relation of Antecedent Egg Production to Sex Ratio 
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a number of workers, Davenport (8, 9, 10, 11), Goodale (16, 17, 18), Hadley (23), 
Pearl and Surface (42, 46), Morgan and Goodale (38), Spillman (50), and Stur- 
tevant (51). The results of these experiments involving the inheritance of sex- 
linked characters are of common knowledge, and their significance from the 
standpoint of the Mendelian inheritance of sex is so well established that nothing 
further regarding them will be said for the present. 
It has been quite clearly established, therefore, that in the case of the domestic 
fowl sex is inherited, under normal conditions, as a Mendelian character. Under 
such conditions chance combination of the germ cells produces equal numbers of 
homozygotes and heterozygotes, which fact explains the approximate equality 
of the sexes. Sex is apparently determined at the time of fertilization and is 
associated with the presence or absence of a second sex chromosome. 
It has been shown in this study that as egg production increases the sex ratio 
decreases. Pearl (45) made a similar observation as a result of an extensive 
study of the relation between egg production and the sex ratio during the normal 
hatching season. It was found that “the larger the number of eggs which a hen 
lays before being put into the breeding pen, the larger will be the proportion of 
females and the smaller the proportion of males produced by her eggs.” It is 
regrettable that shortly after the publication of the brief note concerning the 
nature of his results, all of Pearl’s material bearing on this problem was lost 
through an unfortunate accident. Apparently the decrease of the sex ratio in 
the present study can not be accounted for on the basis of prenatal mortality, 
for it has been shown that prenatal mortality affects the ratio to a slight extent 
only, and to the same extent throughout the year. 
What factors are operative, therefore, in effecting an alteration in the sex 
ratio from an approximate equality of sexes which has been found to exist during 
the normal hatching season? There is a differential hatching rate of the sexes 
between the period of early egg production and the period of later production, 
as shown in Table III. Apparently tha difference in the proportion of sexes 
produced from one period of egg production to another is accounted for by the 
difference in the absolute numbers of sexes produced from one period of egg 
production to another. Since in the domestic fowl the male is homozygous for 
sex, it does not seem probable that the spermatozoa would influence the situa¬ 
tion, at least not from the standpoint of affecting the mechanism of the fertiliza¬ 
tion process. The fertilization process is a reaction process pessessing very 
definite biological and biochemical characteristics, as pointed out by F. R. Lillie 
(33), and although the spermatozoa may provide a stimulus while the egg is still 
in the second maturation stage, there is no known reason why the spermatozoa 
might affect a change in sex determination from one period of egg production to 
another. Bearing on this point, an interesting case has been reported by Hays 
(25) where the amount of sexual service in male rabbits, which are heterozygous 
for the sex character, affects the sex ratio, there being a predominance of males 
in the first service group and then usually an increasing predominance of females 
as the number of services is increased. Hays has mentioned two possibilities to 
account for this situation: 
Either female-producing spermatozoa are formed more largely than male-producing spermatozoa as 
the amount of service of the male increases, or the male-producing sperm are in themselves weaker than 
the female-producing sperm and consequently fewer of them survive to take part in fertilization. 
There is no evidence on the first point, and in connection with the second 
point it is suggested that the female-producing sperm, because of its larger size 
and greater chromatin content, may be more vigorous than the male-producing 
sperm and thus more apt to first reach the egg for the process of fertilization. 
According to unpublished results of Lush, however, there is no apparent differ- 
