An Introduction to a Biology 



I will take an example with which I am familiar. When a 

 yellow-and-white Japanese waltzing mouse is crossed with 

 an albino, a hybrid is produced which is unlike either parent, 

 being, with some exceptions, hardly distinguishable from 

 the common house-mouse (see Bateson, :02, note on p. 55 and 

 pp. 24 and 25). This hybrid (I have bred some 350) is never 

 an albino, and it never waltzes : albinism and waltzing there- 

 fore are recessive characters ; and pigmentation and normal 

 progression are the corresponding dominant characters. So 

 that we are crossing a creature the albino possessing 

 normality of progression (D) and albinism (R) with another 

 beast which exhibits waltzing movements (R) and the pre- 

 sence of pigment (D). Let us consider the offspring of 

 hybrids thus produced from the point of view of the two 

 pairs of allelomorphs. First, with regard to colour, we 

 should expect 25% albinos which should breed true : this is 

 in fact what we get. Secondly, with regard to their pro- 

 gression, we should expect to find 25% waltzing mice : this 

 is very roughly what happens. I have been unable to deter- 

 mine if they breed true (on the Mendelian hypothesis they 

 should, of course). Now let us look at the offspring of 

 hybrids from both points of view at the same time : one 

 mouse in every four is an albino ; one in every four is a 

 waltzer, so we should expect one in every sixteen to be an 

 albino waltzer. Now these albino waltzers are new things ; 

 and, what is more, they should breed true, because both 

 their characters (A and W) are recessive. What has hap- 

 pened is that we have taken the recessive character albinism 

 from one parent of the hybrid, and the recessive char- 

 acter "waltzing" from the other; and through the 

 mediation of the hybrid united them in one individual 

 the new albino waltzer which will produce nothing but 

 offspring like itself, because its gametes are pure. 1 I have 



1 I am not sure that this case is not, strictly speaking, an example of a 

 synthetical variation ; at any rate, it is a very simple instance of the argu- 

 ment set forth in Bateson, :02a, p. 29. 



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