INHERITANCE 713 



produces a clone of large individuals; biotypes of small individuals give 

 clones with small individuals; rapidly multiplying biotypes produce 

 rapidly multiplying descendants; and so on. Such inheritance is shown 

 with respect to vigor or weakness, to resistance and lack of resistance, 

 and to structural and physiological characteristics of all sorts. 



Members of a given biotype, having the same genetic constitution, may 

 differ in ways induced by different environments, or resulting from dif- 

 ferent periods in the life of the individual. Such differences are, as a 

 rule, not inherited in uniparental reproduction ( exceptions are dealt with 

 later). The main classes of non-heritable differences among the indi- 

 viduals of a single biotype are: age differences; nutritional differences, 

 and environmental diversities resulting from differences in temperature, 

 chemical conditions, and the like. 



In addition to these, there are in some species non-heritable diversities 

 of unknown origin between members of the same biotype, the same 

 clone. Thus in Difjlugia corona, which has a silicious shell bearing spines, 

 there are within the same clone differences as to the number and size of 

 the spines borne by the shell. In this case the differences arise at repro- 

 duction, presumably under the influence of environmental diversities. 

 They follow the same rule as known environmental differences; they are 

 not as a rule inherited. If parents with many spines produce descendants, 

 the mean number of spines in these descendants is the same as in the 

 descendants of individuals of the same clone that have few spines (excep- 

 tions noted in later pages) . 



Thus, as a rule, racial or inherited characters are not altered in uni- 

 parental reproduction. This is the most striking and obvious feature of 

 such reproduction. Yet it does not hold absolutely; there are important 

 limitations and exceptions to this rule. A large proportion of our dis- 

 cussion of uniparental inheritance will deal with these exceptions. They 

 are taken up next. 



Changes in Inherited Characters in Uniparental Reproduction 



In a number of different categories of cases, inherited differences arise 

 during uniparental reproduction, so that the members of a single clone 

 are not all alike in characteristics that are inherited in vegetative repro- 

 duction. Some of these phenomena are of great interest for general 

 genetics. They may be classified in various ways. 



