Isozyme markers have several advantages in linkage analyses, especially for agronomic characters controlled by major genes. A large number of the individuals are treated simultaneously, as crude extracts are easily obtained from seedlings or endosperms. Most of the isozyme alleles are codominant, and individual genotypes (homozygotus or heterozygotus at a locus) of the are detected by the banding patterns after electrophoresis. Furthermore, isozyme alleles have no pleiotropic effects on other characters. From these advantages, isozyme loci should be localized on chromosomes as useful linkage markers.
The present authors (1987) found that three loci for esterase isozymes (Est1, Est2, and Est4) are tightly linked and located at a terminal position on the long arm of chromosome 3. Further analysis was conducted to obtain the more detailed information about chromosomal localization of these complex loci for esterase and the aspartate aminotransferase-3 (Aat3) locus. Individual seedlings of F2 populations derived from two crosses (Smyrna × uz-als-cu2 and Punjub T-5 × al-uz-als) were examined for alleles at two isozyme loci and transplanted in the field for observation of marker phenotypes. For some markers, segregation within F3 progenies was investigated at the seedling stage.
F2 and F3 data of a cross between Smyrna and uz-als-cu2 for linkage relationships among Est4 and three loci are presented in Table 1. The complex loci for esterase isozymes are localized at the terminal of the long arm of chromosome 3, and linked with cu2 locus with a recombination value of 25.2% ± 4.1. Meanwhile, linkage data for Aat3 and three loci are shown in Table 2, using F2 and F3 data derived from the other cross between Punjub T-5 and al-uz-als. These data suggest that the Aat3 locus is located between two loci, al and uz, on chromosome 3.
From these results, the arrangement of six loci on chromosome 3 is thought to be al-Aat3-uz-als-cu2-Est4, as shown in Fig. 1. The detailed information about the orientation of these loci and several markers will be obtained from the Coordinator's Report (chromosome 3) in the present issue.
Konishi, T. and S. Matsuura. 1987. Linkage analysis of Est4 locus for esterase isozyme-4 in barley. BGN 17:68-70.