SPECIAL PROBLEMS OF MEIOSIS 87 



species of Oenothera, but not in all. In the re- 

 mainder intermediate stages between this condition 



Two-Strand Pachytene 



c Diakinesis 



b Diplotene 



d First Metaphase 



Fig. 19. — Diagrams of the First Meiotic Division in Oenothera 

 lamarckiana. The chromosomes are labelled 1-14. 

 1 and 2 form a bivalent, being homologous throughout. 

 3-14 form a ring of 12 chromosomes united by 12 

 chiasmata after diplotene. The middle segments contain- 

 ing the velans and gaudens genes are labelled v and g. 

 These segments contain the median spindle attachments. 

 At anaphase chromosomes 3, 5, 7, 9, 1 1 and 1 3 go to one 

 pole, 4, 6, 8, 10, 12 and 14 to the other. 



and normal homozygosity are found. Thus in 

 Oenothera lamarckiana a ring of twelve chromosomes 

 and a single bivalent are formed at meiosis, in Oe. 



