34 THE THEORY OF THE GENE 



This behavior of the chromosomes in the maturation 

 stages parallels Mendel's first law. A chromosome de- 

 rived from the father separates from a chromosome de- 

 rived from the mother for each pair of chromosomes. The 



/ 



«*» 



• .^ 



:*s- 



.ft.,,,.;., a 



\J°</ 



••• b 





Fig. 22. 

 Diagram of two maturation divisions of the egg. The first polar 

 spindle is shown in a. The separation of the paternal and maternal 

 chromosomes (reduction) is shown in b. The first polar body has 

 been given off in c. The second polar spindle is formed in d; each 

 chromosome has split lengthwise into daughter halves (equational 

 division). The second polar body is being given off in e. The egg- 

 nucleus is left in f with the half (haploid) number of chromo- 

 somes. 



f 



germ-cells that result contain one chromosome of each 

 kind. Taking the chromosomes in pairs we may say, half 

 of the germ-cells, when mature, contain one member of 

 each pair, the other half the mates of those chromosomes, 

 pair for pair. If one substitutes Mendelian units for chro- 

 mosomes, the statement is the same. 



