RECIPROCAL TRANSLOCATION 337 



In this way it has been possible to determine the degree of similarity, 

 or relationship, between the various complexes. In a parallel series of 

 cytological researches by Cleland and Oehlkers it has been shown that the 

 chromosome sets carrying the genetic complexes show clearly their degree 

 of relationship in the configurations produced at diakinesis after two 

 such sets have been combined in a cross. Complexes which are closely 

 related genetically combine to form configurations with most or all of 

 the chromosomes in separate pairs at diakinesis, whereas complexes 

 which are more distantly related give configurations with more of the 

 chromosomes involved in circles. The more distant the relationship, 

 the larger the chains or circles. Plants with identical genetic constitu- 

 tions tend to show similar configurations at diakinesis.^" The genetical 

 and cytological data are in striking harmony, which confirms the theory 

 that in these plants several genetic complexes differentiated by rearrange- 

 ment and gene mutation are carried by chromosome sets differentiated 

 largely by reciprocal translocation. 



The development of the chromosome ring in the meiotic prophase of 

 (Enoihera is presumably like that in Zea, where it has been shown that 

 homologous portions synapse laterally and later open to form the ring 

 (p. 331). CEnothera is ill adapted to a study of these stages, but aside 

 from reports of parallelism of prophasic threads^^ there are other indica- 

 tions of lateral synapsis at some stage earlier than diakinesis. Among 

 these are interlocking of ring-shaped bivalents and larger rings and the 

 presence of chiasmata.^^ Moreover, crossing-over has been demonstrated 

 genetically for chromosomes in the ring,^^ which indicates a lateral 

 association. In view of the striking way in which parasynapsis with 

 reciprocal translocation accounts for the phenomena in CEnothera, as it 

 does for those in organisms {e.g., Zea) whose prophasic changes can be 

 clearly followed, this is now generally accepted as the proper interpreta- 

 tion of meiosis in this genus. For many years cytology witnessed a 

 battle between "parasynapsis" (lateral synapsis) and " telosynapsis " 

 (synapsis primarily end to end^^), but the battle has now practically 

 ended with the retirement of telosynapsis from the field as a general 

 interpretation of the meiotic prophase. 



1" See Hoeppener and Renner (1928) and Cleland (1931a) for diagrams of relation- 

 ship of complexes and of chromosome configurations in crosses. 



11 Gates and Goodwin (1931), Weier (19306), S. Emerson (19316). 



12 Catcheside (19316), Darlington (1931e). 



1^ See S. H. Emerson (1931a). Crossing-over between catenated chromosomes 

 has also been demonstrated in Zea, where the parasynaptic condition is particularly 

 clear (Creighton and McClintock, 1931), and in Datura (Blakeslee and Bergner, 1932). 



1* Mid-prophasic doubleness was attributed to splitting rather than synapsis. 

 This interpretation will apply to unsynapsed portions of threads in translocation 

 complexes, multivalents (Fig. 159) and elsewhere, but not to normal meiosis. "Telo- 

 synapsis" of catenated chromosomes is but the result of a restriction of parasynapsis 

 to terminal regions. 



