Cytogenetics of Oenothera 



\6S 



generation after generation in biennis and 

 Lamarckiana. It is a simple matter for you 

 to work out that all the recessive lethal alleles 

 in the one strain cannot be identical to those 

 in the other of these two strains, for the Fi 

 from crossing them would be of only two 

 different phenotypes, whereas three types 

 were actually obtained. We can conclude, 

 therefore, that the balanced lethal system in 

 Oenothera in general involves either a multi- 

 ple allelic series, or several pairs of genes, or 

 both. 



While each of the three different hybrids 

 obtained in Fi from crossing Lamarckiana 

 and biennis breeds true upon self-fertilization, 



showing in this way that each contains two 

 completely linked gene complexes, this may 

 or may not be true of the breeding behavior 

 of hybrids obtained from certain other inter- 

 racial crosses. This ambivalence is illus- 

 trated in Figure 20-5. In this Figure, the 

 gene complexes present in the different hy- 

 brids are shown at the left. The distribution 

 in their gametes of the various genetic markers 

 shown at the top of the Figure was determined 

 by breeding tests. So, for example, the 

 cur vans. velans hybrid bred in such a way that 

 all marker genes behaved as though they 

 were still linked (the marker genes and their 

 alleles being distributed in gametes in a total 



FLAVENS-CURVANS 



FLAVENS-PERCURVANS 



FLAVENS-FLECTENS 



FLAVENS-VELANS 



RUBENS-FLAVENS 



RUBENS-CURVANS 



CURVANS-VELANS 



RUBENS-VELANS 



FIGURE 20-5. Linkage groups in liybr ids from interracial crosses. 



