No. 631] FACTORS OF HEREDITY 



10] 



bound, in segregation, with only two others— in bipolar 

 fashion — so that the whole group, dynamically consid- 

 ered, is a chain. This does not necessarily mean that the 

 spatial relations of the factors accord with these dynamic 

 relations, for it is conceivable a priori that factor A 

 might be far off from B, in another part of the cell, or 

 that both might be diffused throughout the cell, and that 

 they might nevertheless attract each other, during the 

 segregation division, by some sort of chemical or physical 

 influence. In the discussion that follows, no implication 

 as to the actual physical arrangement of the genes is in- 

 tended when the terms ' ' linear series,' ' " distance," etc., 

 are used; these will refer only to the relations existing 

 between the points in the linear map, which may be re- 

 garded merely as a mathematical mode of representa- 

 tion of the data themselves. It will be shown, however, 

 at the conclusion of this article, that when the various 

 conditions which have to be fulfilled at segregation are 

 taken into consideration, any other explanation for these 

 peculiarly linear linkage findings than an arrangement 

 of the genes in a spatial, physical line proves to be haz- 

 ardously fanciful. 



In the case of the larger distances, in order to discover 

 what function of the distance the per cent, of separation 

 represents, it w T ould be necessary to conduct extremely 

 delieate determinations, involving very extensive data in 

 experiments dealing with many points simultaneously. 

 Nevertheless enough has been done to show that even for 

 the larger distances the per cents of separation do de- 

 pend on the distance in the linear map-being less than 

 the distance by an amount which varies in a fairly regu- 



known that the higher per cents of separation certainly 

 involve some function of the linear distance. 



In the case of the smaller distances, on the other hand, 

 the function has been rather accurately ascertained; it 

 is very close to the simplest one possible, that is, there is 

 an almost exact proportionality here between the map 



