SEX-LIMITED INHERITANCE IN POULTRY 6 



symbolical of the presence of two sex-limited characters. The 

 presence of a determiner for a sex-limited character is indicated 

 by a solid symbol ; the absence of the determiner by a hollow sym- 

 bol. The absence of a sex-chromosome is represented by a 

 dotted circle without included determiner. 



Let 1 and 2 represent the sex-chromosomes of the sperm cells 

 of one race, present and alike in all the sperm. Let 3 represent 

 from another race, one of the eggs that contains the sex-chromo- 

 some and 4 one of the eggs that is without it. Let the two kinds 

 of eggs be equally numerous and equally apt to be fertilized. By 

 the theory the union of two germ-cells that both contain sex- 

 chromosomes determines a male; the fertilization of an egg that 

 lacks a sex-chromosome by any of the sperms determines a female. 

 It is clear that, in the male progeny, determiners for sex-limited 

 characters come from both germ-plasms and the sons show the 

 dominant sex-limited characters of both races; on the other hand 

 the daughters show the sex-limited characters of their sires only. 

 It is easy to see that in a reciprocal cross the sons will show the 

 same characters as before but the daughters, inheriting their sex- 

 limited characters solely from their fathers, will be different 

 because they have different fathers. 



3. SEX-LIMITED CHARACTERS HERETOFORE DESCRIBED OF 

 THE TYPE SHOWN BY POULTRY 



1. The first case of sex-hmited inheritance in the modern sense 

 that was worked out by modern methods of analysis and with an 

 approximation to the modern interpretation was, as is well known, 

 that of the English current moth, Abraxis grossulariata, and its 

 variety, lacticolor. This brilliant achievement of Doncaster 

 and Raynor ('06) marks an epoch. According to our present 

 interpretation this case is simply one in which the variety (lac- 

 ticolor) has arisen by the dropping out of a factor, G, possessed 

 by the grossulariata, so that lacticolor may be represented by g 

 (table 1). 



The results of Doncaster and Raynor agree closely with ex- 

 pectation as indicated at the right of table 1, and sustain the 

 hypothesis that in the female the sex-determiner is simplex. 



