CHAPTER VI 
CYTOPLASMIC INHERITANCE 
When a sperm, bearing a known dominant gene 
for an embryo-character, fertilizes 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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