J24 Hagedoorn. 



stood the facts, which, I admit, were not too clearly stated, I think 

 it well to repeat the evidence here. 



The family in which the mutation occurred was homozygous for 

 the presence of G, and consisted of agoutis and albinos, abcdefgh 

 and aBCDEFGH. 



It originated from a wild agouti and an albino, aBCDEFGH. This 

 family was inbred throughout a great number of generations, each 

 pair consisting of brother and sister. This circumstance proved to be 

 very valuable, for, when at a given moment there were black young 

 (ABCDEFgH) produced in this family, these blacks had only two grand- 

 parents, two great-grandparents and so on, and it was a comparatively 

 simple matter to test all these ancestors by suitable testmatings. 



To test these animals I mated each one of them to either a 

 black or a chocolate one. In this way it is easy to distinguish an 

 AABBCCDDEEFFGGHH mouse from an AABBCCDDEEFFGgHH one, the 

 former giving only agouti (cinnamon agouti) young, the latter giving 

 agouti (cinnamon) and black (chocolate) young in equal numbers in 

 such a testmating. 



The numbers of young produced from each testmating always 

 exceeded eight, and the two animals of which one must have given 

 off at least two gametes devoid of G gave in testmatings alone thirty- 

 four and twenty-seven young respectively, all of which had G. 



Plate, who does not seem to have quite understood my state- 

 ment in the preliminary communication of this case, that the black 

 mice produced had only two ancestors in each of several preceding 

 generations, two grandparents, great-grandparents and so on ("because 

 of inbreeding there were only two of each preceding generation") 

 believes that I have worked out these testmatings with very small 

 numbers. It is for that reason that I now give the exact numbers, 

 which, I hope, will be found amply sufficient. 



The facts are simply these : One couple of agouti mice were mated. 

 They were of the constitution AaGG and gave six agouti and two 

 albino young. One of these agoutis proved later to be a heterozygote 

 for G, being Gg. One of the albino young in the same litter proved 

 also to be a heterozygote for G, being aaGg. 



This heterozygous nature of these two young produced from 

 homozygous parents can only be explained by assuming that one of 

 the parents had produced at least two gametes without o. Never- 

 theless this parent ordinarily gave only gametes containing the 

 factor G, as can be seen from the testmatings. 



