304 EVOLUTION AND GENETICS 



In other details of inheritance such as hnkage, crossing over and 

 sex-linkage the parallel is found to hold true. Behaviour of unit 

 characters, however intricate, is found to be closely in accordance 

 with the behaviour of the chromosomes as established by cyto- 

 logical studies. 



Every known fact concerning the structure and function of 

 the chromosomes singles them out as the seat of the hereditary 

 properties of the organism. They are not independent of the 

 cytoplasm, but are rather a controlling center. As the artist needs 

 a medium of expression, so must they use the cytoplasm as a 

 medium for the production of structures in the individual. There 

 is nothing to show that other parts of the cell exert a shaping 

 influence in themselves. 



Summary. The chromatin contained in the nucleus of a cell 

 is made up of many granules called chromomeres which are 

 aggregated during cell reproduction to form chromosomes. The 

 behaviour of these bodies follows a definite plan in ordinary cell 

 reproduction and in the sexual reproduction of the individual. 

 In sexual reproduction germ cells are formed which may differ in 

 everything but chromosome content. This alone is the same in 

 all germ cells of a species, with the exception of sex chromosomes. 

 Since the heritage is derived equally from male and female parents, 

 it is logical to interpret the chromosomes as its physical basis in 

 the germ cells. Moreover the behaviour of the chromosomes in 

 reproduction is so much like the behaviour of unit characters in 

 the course of heredity as to establish the theory beyond reasonable 

 doubt. The chromosomes are now commonly interpreted as the 

 conveyors of determiners of hereditary characters, and there is 

 no evidence to show that other parts of the cell act in a similar 

 capacity. 



REFERENCE 

 McClung, C. E., Cowdry's General Cytology, Section X, 1924, 



