712 INHERITANCE 



vides, each gene divides — one product from each going to each of the 

 two offspring. In the cihate Infusoria, the macronucleus not only divides 

 but is in many cases reorganized (see Chapter XIII). The cytoplasmic 

 body divides and is to a great extent (or entirely) reorganized. The 

 general upshot is that the constitution of nucleus and cytoplasm is typi- 

 cally the same in the offspring as in the parent (exceptional conditions 

 are dealt with in later pages) . 



INHERITANCE OF CHARACTERISTICS 



Clones. — All the individuals produced by uniparental reproduction 

 from a single individual are known collectively as a clone. The general 

 rule for inheritance in uniparental reproduction fs that all members of 

 the clone are alike in genetic constitution and in inherited characteristics. 

 That is, the new individuals (clone) produced from a single parent are 

 like the parent and like one another in their characteristics, structural and 

 physiological. Taken together, they form the equivalent of a set of iden- 

 tical twins. 



There are numerous exceptions to this rule of the genetic identity of 

 parent and offspring in uniparental reproduction, and these are among 

 the most important and interesting phenomena of genetics. They are 

 dealt with fully on later pages. But the relation of identity of genetic con- 

 stitution in parent and offspring holds for perhaps 99.9 percent of all 

 cases; it is the most striking feature of uniparental reproduction. 



Certain manifestations of this principle of identity in genetic consti- 

 tution between parent and offspring require special consideration: 



1. Biotypes. In all Protozoa fully studied, any species consists of a 

 great number of diverse biotypes — races differing in inherited character- 

 istics. The different biotypes may differ in size, form, structure, and 

 physiology (rate of multiplication and the like). Such diverse biotypes 

 in Paramecium, Difjiugia, Arcella, and other Protozoa are described and 

 illustrated in the present author's Genetics of the Protozoa (1929). 



When individuals of diverse biotypes reproduce uniparentally, as by 

 fission, the general rule is that each biotype retains its characteristics. 

 The offspring are like the parents in all conspicuous respects. Thus all 

 members of a single clone belong to the same biotype and have the same 

 inherited characteristics. In biotypes of large individuals, each individual 



