NATURE OF PLANTS 



141 



nuclei is shown at the right and left of figure four. In this way 

 the red factor comes to be lodged in one of the daughter cells 

 and the white factor in the other daughter cell. This separation 

 of the factors that appear in the two members of a pair of chromo- 

 somes is termed the segregation of the factors. It is one of the 

 most important features in the cell divisions that result in the 



R 



FIG. 865. 



Diagram of a nucleus showing mode of division in gamete 

 formation. See text. 



formation of the gametes. The members of a pair of chromo- 

 somes are termed homologous chromosomes and the contrasting 

 factors which they bear, in this case red and white, are named 

 allelomorphs. We see that it is the behavior of the homologous 

 chromosomes and their allelomorphic factors that determine the 

 nature of the gametes. 



The fundamental features to note in the above discussion is 

 first that the factors remain distinct and show no indication of 

 fusing with one another. The red and white factors appear 

 unchanged in the gametes no matter how many crossings have 

 been effected. The second feature is that these factors, though 

 associated in pairs in the homologous chromosomes, undergo at a 



