Two Pairs of Genes in Two Pairs of Autosomes 125 



somes is entirely independent of the segregation of the Cr and 

 cr chromosomes, so that four types of gametes will be produced 

 by the Fi plant in equal numbers. 



Once the maternal and the paternal chromosomes enter the 

 Fi their identity as maternal and paternal chromosomes is en- 



7 



10 



Fig. 38. Diagram of the ten chromosomes of Zea mays showing the 

 relative mean length at midprophase I. The centromeres (kinetochores) 

 are indicated by open circles, the known knob positions by black circles, 

 and the nucleolus-organizing body by stippling. (Redrawn from Longley 

 in the Botanical Review.) 



tirely lost. The way the homologues of one pair separate is 

 entirely unaffected by the way the homologues of any other pair 

 separate. It is purely a matter of chance whether an Fi gamete 

 which has a "maternal" chromosome III will also have a "ma- 

 ternal" chromosome VI or whether it will have a "paternal" 

 chromosome VI. Since it is entirely a matter of chance, the four 

 types of gametes will be present with equal frequency, within 



