Wilson — Agouti-black Colour in Babbits. 595 



neighbour black groups, that the total number of matings was small, and 

 that the true colours of the Himalayans were not identified and counted — an 

 important matter wben the numbers are small. Yet a fair comparison can 

 be made between the expected and the experimental results. 



Since the group y was not clearly separated from its black neighbours, 



we must see which other groups were mated alongside it. When the other 



X' X. 

 heterozygous group agouti-black, y , was mated with heterozygous yellow, 



blacks and agoutis were produced in the ratio 5 : 3. The blacks so produced 



were ^'* ^-'^ ^'* ^^, in the proportion 1:2:1:1.' A set of blacks 

 TY Yy tj y yif ^ ^ 



produced in tliis way was mated with chocolate,^ whose constitution so far as 

 this experiment is concerned is . From this mating the first group, yy, 



should produce agoutis and agouti-blacks in equal proportions, the second 



X! X 



y — which is the other group heterozygous for two pairs of factors — should 



produce blacks, agoutis, and agoiiti- blacks in the ratio 2:1: 1 ; the last two 

 groups should produce blacks only ; and the relative proportions of the 

 parents producing progeny in these three groupings should be 1 : 2 : 2. The 

 experimental results are' : — 



Numbers of Parents. Progeny Produced. 



X' X 

 Thus, although y ' was not separated from its neighbours in this mating, 



the experimental results are approximately as they sliould have been 



had y and its neiglibours been bred in the usual way and produced in 

 the usual proportion. 



But another mating was made with a similar set of blacks, excepting that 

 those capable of producing blacks only from chocolate were eliminated. The 



X' X X' X 



groups mated were, therefore, yy and y ' , and the numbers in the 



former should have been to those in the latter in tlie ratio 1 : 2. They were 

 mated with heterozygous yellow. The former group should have produced 



' See top of previous page. - Journal of Genetics, vol. ii, p. 233. ' Ibid. p. 233. 



