Synaptonemal complex karyotyping: an appraisal based on a study of Crepis capillaris

A synaptonemal complex (SC) karyotype for Crepis capillaris, based on SC measurements from 92 surface-spread pachytene nuclei, was compared with the mitotic karyotype of this species in order to evaluate the specific and general validity of SC karyotyping and to assess its potential for high resolution physical mapping. Although there are obvious similarities between the SC and mitotic karyotypes of Crepis capillaris, detailed quantitative comparisons reveal that they differ in some respects, both with regard to the relative lengths of entire chromosomes and arm ratios. The arm ratio differences between SC and mitotic chromosomes are evident in both the A and C chromosomes and reflect the distribution of C-banding heterochromatin. Based on this comparison, heterochromatin appears to be underrepresented in SC length. However, the relative lengths of entire A and C chromosome SCs do not conform to this model and suggest that some other factor or factors are also influencing SC lengths differentially. It is concluded that the non-agreement of SC and mitotic karyotypes does not invalidate the use of SCs for karyotyping and physical mapping purposes provided that any differences are understood and characterized as far as possible.