An Introduction to a Biology 



germ-cell of a pea, whether it be contained by the pure 

 yellow or pure green race, or by the hybrid or any of its 

 descendants, is absolutely pure. And it is believed that it 

 will continue to be pure in respect of these characters until 

 a specific upheaval takes place, when a new character will 

 arise by the process of discontinuous variation. 



(6) The second is the conception of unit-characters (I.e., 

 pp. 27-28) in respect of which the gamete is pure. Such 

 units seem to correspond to that in the adult organism which 

 Weismann sought in the germ. These unit-characters, as 

 we have seen, usually exist in pairs in such a way that one 

 is dominant and the other recessive ; and this fact is recog- 

 nised by naming such characters allelomorphs. It is hardly 

 necessary to say that the germ contains not merely one allelo- 

 morph (as we have been imagining for the sake of simplicity), 

 but very many ; in fact, Mendel recognised seven such pairs 

 in his peas, and this must be the merest fraction of the 

 actual number that exists. 



(c) We are thus indirectly led to the conception of " com- 

 pound characters, borne by one gamete, transmitted entire as 

 a single character so long as fertilisation only occurs between 

 like gametes" (I.e., p. 29). The reader is here strongly 

 advised to refer to the first thirty-five pages of Bateson's 

 book (Bateson, :02a). 



(8) THE RELATION BETWEEN THESE NEW CONCEPTIONS AND 

 THE THEORY OF THE ORIGIN OF SPECIES BY DISCON- 

 TINUOUS VARIATION (a, GAMETIC PURITY ; b, UNIT- 

 CHARACTERS ; c, COMPOUND CHARACTERS). 



Let us suppose a new character to arise by discontinuous 

 variation ; for example, the possession of a trunk in a race 

 of previously snoutless elephants. According to the statis- 

 tical view of heredity this new character would be soon 

 swamped by the, so to speak, normal trunkless ancestry of the 

 new form itself and of its mate ; for one of two courses is 

 open to the new form ; it may either unite with another like 



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