INHERITANCE 711 



(genes or factors) reproduce themselves true to type, in development 

 and reproduction. Each kind of genetic material assimilates, producing 

 more material of its own type, and each unit of material, or gene, pro- 

 duces at division new units like itself. 



The Protozoa have chromosomes that are similar to those in other 

 organisms (see Chapter XII). One question that arises in protozoan 

 genetics is this: Are there in the Protozoa other genetic materials in ad- 

 dition to those in the chromosomes, having the two essential properties 

 just mentioned? 



Types of Reproduction and Inheritance 



In the Protozoa, as in some other organisms, there are two main types 

 of relation of offspring to parents: 



1. Uniparental reproduction; offspring arise from a single parent, as 

 in the various types of vegetative reproduction. 



2. Biparental reproduction; offspring are formed from the combined 

 parts of two parents, as in sexual reproduction in the Protozoa by copu- 

 lation, conjugation, and the like — followed by division. 



The two kinds of reproduction differ fundamentally in their relation 

 to the genetic constitution, or genetic materials (chromosomes and their 

 genes). In uniparental reproduction, typically each of the genetic mate- 

 rials of the parent is divided and duplicated, so that the genetic consti- 

 tutions of offspring are like those of their parents. In biparental repro- 

 duction, the complex of genetic materials present in each of the two 

 parents is taken apart, and a new combination is made from parts of 

 these. The genetic materials of the offspring are a new combination of 

 those of the two parents. 



In consequence of these differences, uniparental and biparental repro- 

 duction give very different consequences in inheritance. The two will 

 therefore be dealt with separately. 



Inheritance in Uniparental Reproduction 

 material processes 



Details as to the material processes in uniparental reproduction are 

 dealt with in other chapters (see Chapters XIII and XIV) . The essential 

 features, for genetics, are that the nuclei divide, each chromosome di- 



