MENDELIAN SEGREGATION 3 
corresponding unit derived from the mother. These 
units will henceforth be spoken of as factors; the 
two factors of a pair are called allelomorphs of each 
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Fig. 1.—In the upper line, four stages in the division of the egg (or 
of a body cell) are represented. Every chromosome divides when the 
cell divides. In the lower line the ‘‘reduction division” of a germ cell, 
after the chromosomes have united in pairs, is represented. The mem- 
bers of each of the four pairs of chromosomes separate from each:other at 
this division. 
other. Their separation in the germ cells is called 
segregation. 
The possibility of explaining Mendelian phenomena 
