304 CHROMOSOMES IN HEREDITY : PHYSIOLOGICAL 



nucleolar production associated with secondary constrictions 

 (Ch. II). This now requires more detailed consideration. 



(ii) Organisation of Nucleoli. McClintock (1934) has carried out 



VI— IX 



IV— VI 



IV— VI 



Fig 



99. — Diagrams of pachytene in Zea Mays. I, homozygous 

 pair showing non-homologous torsion-pairing of chromosomes 

 with themselves. VI — IX, interchange involving the nucleolar 

 organiser at which the exchange of partner would occur but for 

 non-homologous pairing. IV — VI, interchange without (left) 

 and with (right) non-homologous pairing. The relational 

 coiling associated with torsion-pairing is not shown, x 1200 

 (McClintock, 1933). 



an analysis which makes it possible to define the factors controlling 

 nucleolar production at the second telophase of meiosis in Zea. 



