GENETIC SYSTEM: RELATION TO CHARACTERISTICS 1 05 



of the developing individual. In Drosophila, if the number 

 of sets of autosomes, in relation to the number of X's, is 

 changed, this changes the sex (see Chapter III). 



Do autosomes also affect other characteristics? Do the 

 different pairs of autosomes have different functions? Are 

 there diverse types of autosomes, with different effects, in 

 different individuals of a species, as is the case in relation to 

 the X-chromosomes? Are there dominant and recessive ef- 

 fects of autosomes, as there are of X? 



If dominant and recessive characteristics depend on auto- 

 somes, then these characteristics must follow the distribu- 

 tion of the autosomes from parents to offspring, as the 

 characteristics dependent on X follow its distribution. We 

 must then examine the method of distribution of the auto- 

 somes, to see whether there are characteristics that show 

 this method. 



Method of Distribution of the Autosomes: The distribu- 

 tion of the autosomes from parents to offspring is much 

 simpler than that of the X-chromosomes. The main facts 

 are as follows : 



1. The autosomes are in pairs in all individuals (figures 

 3, 6, 7). There are no individuals with unpaired autosomes, 

 like the male of some organisms with relation to X. 



2. Thus the two sexes are alike as to their autosomes. 



3. In forming germ cells, one member of each pair of 

 autosomes goes to each germ cell (figure 4). The sperms 

 and the ova are alike with respect to the autosomes. 



Thus the fundamental rule with relation to the auto- 

 somes is that each germ cell carries one member of each 

 pair of autosomes. 



4. By union of two germ cells the pairs of autosomes are 

 restored (figure 5 ). 



5. Thus each one of the offspring carries In each pair of 

 its autosomes one autosome from each parent. 



Now consider a single pair of autosomes, such as the pair 



