210 GENETICS 



Ay 3. Sex Chromosomes in Parthenogenesis 



The behavior of the chromosomes in cases of 

 parthenogenesis, where the union of an egg-cell and 

 a sperm-cell are not necessary for the production 

 of a new individual, throws additional light upon 

 the relation between chromosomes and sex determi- 

 nation. 



For instance, among the social Hymenoptera, bees, 

 ants, wasps, etc., the "queen" produces eggs which 

 upon maturation, if unfertilized, develop into males 

 or drones, all of whose cells contain a reduced amount 

 of chromatin (Fig. 63). It is only when sexual repro- 

 duction occurs through the union of a mature egg- 

 cell and a mature sperm-cell or spermatozoan, that 

 the full complement of chromatin is restored to the 

 fertilized egg and females are again produced. 



Castle says : "In all known cases of parthenogenesis 

 the female is in the duplex (2 n) condition, and the 

 male is in the simplex (n), or partially duplex (2 n — 1 

 condition. The female in all cases has the greater 

 chromatin content." 



b. Castration and Regeneration Experiments 



Certain characters which are known as "secondary 

 sexual characters," such as the ornamental plumage 

 in male birds, the beard in man or the sting in worker 

 bees, are often associated with a definite sex. When an 

 individual is castrated, it is quite common not only 

 for these peculiar secondary sexual characters to dis- 

 appear, but also for the secondary sexual characters of 



