Giemsa C-banding of barley chromosomes

Giemsa C-banding was applied to somatic metaphase chromosomes of 70 reciprocal translocations of barley. Hordeum vulgare L. Based on changes in C-banding patterns in combination with changes in arm ratios, if necessary, breakpoints were localized precisely in 16, and to smaller or larger chromosome segments in 36 translocations. In 18 symmetrical translocations, chromosomes with interchanges could not be identified, because breakpoints were distal to marker bands. Especially with asymmetrical translocations the use of C-banding can assign breakpoints to chromosomes and chromosome arms sooner and often more precisely than currently used procedures. Breakpoints were equally distributed among short and long arms, but with a surplus at centromeres. Translocations with breakpoints in two short arms, a short and a long arm, and two long arms, respectively, were found in a 1:2:1-ratio indicating that arms combined at random. All breakpoints were located in interband regions. The karyotype of one translocation only had a semidicentric chromosome; in another, one chromosome had a persistent gap. Translocations used in cytogenetic studies had a high frequency of asymmetrical interchanges with more distal breakpoints than little-studied translocations. A possible translocation tester set with cytologically distal breakpoints is presented.