INDEPENDENT MENDELIAN INHERITANCE ti 
egg and sperm cells in J’, and these give red-cyed females half of which 
are homozygous (WX)(WX) and half heterozygous (IWX)(wX) and 
equal numbers of red-eyed and white-eyed males (WX)Y and (wX)Y 
respectively. 
In the reciprocal cross, Fig. 36, the white-eyed female contains two 
X-chromosomes each bearing a factor for white eyes. Her genetic 
constitution, therefore, is (wX)(wX). All the eggs from such a female 
will be of the genetic constitution (wX)—they contain an Y-chromosome 
bearing a white-eye factor. When such eggs are fertilized by an X- 
bearing sperm cell from the male, the female produced will be of the 
genetic constitution (IWX)(wX). It will be red-eyed because of the red- 
eyed factor carried by the X-chromosome of the sperm. On the other 
hand, when such an egg is fertilized by a Y-bearing sperm cell, the male 
thus produced will be of the genetic constitution (wX)Y. It will be 
white-eyed, because of the white-eye factor in the X-chromosome of the 
egg-cell.. Breeding two such F individuals together will result in the 
F, distribution shown in the diagram. Females will be produced half 
of which are of the genetic constitution (WX)(wX) and half (wX)(wX), 
hence red-eyed and white-eyed respectively; and males half of the genetic 
constitution (WX)Y and half (wX)¥, hence red-eyed and white-eyed 
respectively. The peculiar relations exhibited in the inheritance of 
white-eye color in Drosophila, therefore, admit of a logical chromosome 
interpretation, if we assume that the factors involved are borne by the 
X-chromosomes. The type of inheritance which is apparently dependent 
on factors borne in the sex-chromosomes is called sex-linked inheritance. 
It will be treated more fully in Chapter XI. 
Mathematical Adequacy of Mendelism.—Mendelian principles do 
not apply to isolated phenomena of inheritance alone, but they are of 
general significance. It is consequently of interest to know how well 
experimental results agree with theoretical expectations when Mendel- 
ian analyses are rigidly applied. Particularly is this true of the mathe- 
matical relations involved, which have often been used to confute the 
arguments of Mendelian interpretations. We shall accordingly con- 
sider the results of Mendel’s original investigation from this standpoint, 
and a few other cases which have been investigated in particularly large 
progenies and under circumstances which practically eliminate personal 
bias. 
Mendel’s investigations with peas included a consideration of seven 
pairs of contrasted characters as follows: 
1. The Difference in Form of Ripe Seeds——These are either round 
or roundish, the depressions, if any, occur on the surface, and are at most 
only shallow as in the indent type; or they are irregularly angular and 
deeply wrinkled. 
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