66 LINKAGE 
factors but were of a random sort, these relations 
could not be calculated from a linear map. 
As a concrete illustration of the way in which a 
group of factors behaves as a linear series, attention 
may be called to the manner of distribution of the 
factors among the germ cells of a female heterozygous 
for a large number of factors in the same pair of 
chromosomes. Let us write the factors derived from 
one parent, 2.e., those in one of the chromosomes, on 
one line (see formula p. 67), in the order which they 
have on the map (see frontispiece), and the allelo- 
morphic factors derived from the other parent, 7.e., 
those in the homologous chromosome, in correspond- 
ing positions on the line below. Then in such a case 
the mature eggs contain either all of the factors 
represented on one line and none of those on the other, 
or they contain all of the factors present in one section 
of the line, and all of the factors present in the re- 
maining section of the other line. In other words, 
the factors obviously stick together in sections ac- 
cording to their position in the linear series. When 
double crossing over occurs the line is broken in two 
places, but even here whole sections remain intact. 
The above facts may be illustrated by an actual 
case. The first formula shows the composition of 
a hybrid female which has received from her mother 
the mutant factors: yellow, white, abnormal, bifid, 
vermilion, miniature, sable, rudimentary, and forked, 
and from her father the normal allelomorphs of these 
factors, together with the dominant mutant factor, 
bar. 
