CHAPTER VI 

 CYTOPLASMIC INHERITANCE 



When a sperm, bearing a known dominant gene 

 for an embryo-character, fertiUzes an egg, the 

 embryo may show only the recessive character of 

 the mother's race. The rate of cleavage of the egg 

 is a case in point. These results are explicable, 

 because the egg cytoplasm has already developed 

 under the influence of the duplex maternal chro- 

 mosomes. On the other hand there may be self- 

 perpetuating bodies in the cytoplasm of the egg 

 that are responsible for certain characters, such as 

 the chlorophyll plastids. Both of these phenomena 

 are here described as cytoplasmic inheritance. 



The interpretation of Mendelian inheritance on a 

 chromosomal basis by no means excludes the possi- 

 bility that there may be other forms of inheritance 

 depending on other cell materials. Although the 

 cytoplasm is essential for the development of the 

 organism, and is transmitted by the egg to each new 

 generation, its substance does not perpetuate itself 

 unchanged as do the chromosomes, and it is therefore 

 really not inherited. There are, however, certain 

 bodies carried by the protoplasm, such as plastids 

 (possibly also chondriosomes) , which, like the chro- 

 matin, are able to grow and divide, and hence might 

 have the power to perpetuate themselves unchanged 



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