The Cellular Basis 



egg is fertilized by a sperm with one of these determiners a fe- 

 male is produced, if by a sperm without the sex determiner a male 

 results. This is graphically illustrated in Fig. 57 in which X 

 represents the sex-determiner, which is duplex in the female and 

 simplex in the male, and the chance unions of male and female 

 germ cells yields females (XX) and males (XO) in equal num- 

 bers. Of course there is no such thing as a "sex-producing" 

 chromosome, sex being a developed character which is the result 

 of many intrinsic and extrinsic causes. The A" chromosome is 

 only one factor in the development of sex but if it is a factor 

 which differs in the case of the two sexes, it is a "sex-differential." 

 2. Environmental Influence. Alteration of Sex Ratios. On 

 the other hand there are many observations which seem to indi- 



Garnetes 



FIG. 57. DIAGRAM SHOWING SEX AS A MENDELIAN CHARACTER, the female 

 being homozygous, the male heterozygous for sex. The female forms 

 gametes all of which contain the X chromosome ; the male forms two sorts 

 of gametes one-half of which contain the X chromosome and the other 

 half lack it. All possible combinations of these gametes give 2:2 or i: I 

 ratio of females to males. 



