20 MENDELIAN SEGREGATION 
matozoon will produce a white-eyed son, because the 
only X chromosome that the son contains is derived 
from his mother, both of whose X chromosomes carry 
a white-producing factor. 
When these red-eyed daughters and white-eyed 
sons are inbred the possible combinations are shown 
in the lower line of the diagram (Fig. 10). 
There will be two kinds of eggs, one containing a red- 
bearing, the other a white-bearing, X chromosome. 
The female-producing spermatozoa will contain a 
white-bearing X chromosome; the male-producing 
spermatozoa will contain a Y chromosome. A red- 
bearing egg fertilized by a female-producing sper- 
matozoon will produce a red-eyed female; a white- 
bearing egg fertilized by a female-producing spermato- 
zoon will produce a white-eyed female. A red-bear- 
ing egg fertilized by a male-producing spermatozoon 
will produce a red-eyed male; a white-bearing egg 
fertilized by a male-producing spermatozoon will 
produce a white-eyed male. The resulting ratio is 
1 red to 1 white, in both sexes. _ 
The distribution of the chromosomes explains how 
in one cross the Mendelian ratio of 3:1 obtains, and 
also how in the reciprocal cross there is a 1:1 ratio. 
Tue INHERITANCE OF Two or More INDEPENDENT 
Pairs oF Factors 
The application of the chromosome hypothesis 
to crosses between races that differ in two pairs of 
factors is illustrated by the following example (Fig. 
