Vol. LI October, 1926 No. 4 



BIOLOGICAL BULLETIN 



GENETIC STUDIES IN POULTRY. 1 

 I. THE SEX RATIO IN THE DOMESTIC FOWL. 



W. V. LAMBERT AND C. W. KNOX. 



INTRODUCTION. 



In comparison with mammals the sex 'ratio in birds has been 

 studied by relatively few investigators. The first report on the 

 sex ratio in birds appears to have been made by Darwin in 1871. 

 He noted that the per cent, of males to females in 1,001 chickens 

 raised by Stretch was 48.65. Field (1901) in 2,105 chickens 

 reported a sex ratio of 44.63, Thomsen (1911) in 805 observations 

 a sex ratio of 47.82, Pearl (1917) in 22,791 cases a percentage of 

 48.57 males, Crew and Huxley (1923) a sex ratio of 49.26 in a 

 total of 753 chicks and embryos examined, Jull (1924) a sex ratio 

 of 48.88 on 2,396 individuals sexed, and Mussehl (1924) a per- 

 centage of 52.24 males from a total of 1,514 chicks upon which 

 observations were made. In pigeons Cole and Kirkpatrick 

 (1915) found that the per cent, of males to females was 51.06 

 on a total of 1,800 squabs and embryos examined. 



The above data represent the total ratios observed by the 

 various investigators on living chicks and dead embryos. With 

 respect to the prenatal sex ratio, however, the data are less 

 extensive, although the sex of the chicken may be quite readily 

 told macroscopically by the ninth day of incubation. Of those 

 reporting on the prenatal sex ratio, Pearl (1917) has the most 

 extensive data, and he gives a sex ratio of 48.3 from a total of 

 1,921 embryos dying between the tenth day of incubation and 



1 Paper No. 12 from the Department of Genetics cooperating with Poultry 

 Husbandry, Iowa State College, Ames, Iowa. The writers are indebted to Professor 

 H. A. Bittenbender for permission to use the material for this study and to Doctor 

 E. W. Lindstrom for valuable suggestions. 

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