No. 570] FACTORS GOVERNING DISTRIBUTION 



343 



general reduction tends considerably to favor the males, 

 while addition favors the females to a slight extent. 



In my previous paper (p. 264) is given in detail a 

 record of the progeny of a female L. sericata (1912-c) 

 lacking both of the first and the right second post-acros- 

 tichal (3, 2, 1, 3). These were inbred to the third gen- 

 eration, in all cases brother being mated with sister in an 

 attempt to analyze the stock as thoroughly as possible 

 and to reduce heterozygosis of factors. 4 Here again, due 



"The importance of mating sisters with brothers for along series of 

 generations in the experiments aimed to detect Mendelizing units of inherit- 

 ance and analyze groups of them, quite generally seems to have been over- 

 looked. As first shown by Castle ('03), random mating of the individuals 

 of successive generations beyond Fi tends to produce in each generation a 

 population with the same per cent, of homozygosis and heterozygosis nil 



for the other factor, and 50 per cent, heterozygous for both. Such a system 

 of random matings often has been confused with the more restricted system 



" It is evident that if A and B are an allelomorphic pair the F, zygotes, 

 resulting from a mating of AA with BB, will be AA, 2AB and BB. 

 Further, if these are all females and are mated in all possible ways with the 



with A A, and one sixteenth will be BB with BB. One eighth of the matings, 

 then, will be homozygous and produce only homozygous young, which, be- 

 cause of the restricted system of mating only sisters with brothers, will pro- 

 duce, in turn, only homozygous matings. The remaining matings, seven 

 eighths of the total, will produce various proportions of homozygous and 



eighth of these matings will be homozygous and seven eighths heterozygous. 

 This would mean that the proportion of heterozygous matings between indi- 

 viduals of the F„ generation would be (7/8)"- 1 . Accordingly one would ex- 

 pect an automatic increase in homozygosis. The expectation is justified al- 



"Dr. Raymond Pearl first published the figures exactly expressing the 



forms is impossible. When I read the October 



