II. 26. Linkage studies in an interchange involving chromosome 6 and 7.
G. Prasad, Dept. of Agricultural Botany, S.D.J. Post Graduate College, Chandesar, Azangarh, U.P. 276128, India. "R"
The interchange line T 6-7 was originally induced through gammarays and chromosomes were identified with the help of translocation testers by Dubey (1969). This line was crossed with linkage testers carrying the following markers:
Chromosome 6 : orange lemma ( o )
Chromosome 7 : short haired rachilla ( s ) and smooth awns (
r ).
The genotype of the interchange line was 0 (green lemma), S (long-haired rachilla) and R (rough awns). The method presented by Joachin (1947) was applied for linkage studies.
Partial sterility (PS) showed 6.36 + 2.55 percent recombination with o (Table 1). Since o is reported to be located near the centromere, the region between this gene and breakpoint will always lie in the interstitial segment, irrespective of the arm carrying the break, and it will always show close linkage with PS. From this data, the breakpoint could not be assigned to any particular artm of chromosome 6. Recombination values of PS with s and r were 7.51 + 2.88 and 15.56 + 3.80 percent, respectively (Table 1). These genes were placed 25 crossover units apart (Robertson, 1971; Prasad and Das, 1976), s being proximal and r being distal to the centromere. The results indicated that the break had occurred between s and r loci on the long arm of chromosome 7.
Table 1. Recombination values between interchange breakpoints and genetic markers.
References:
Dubey, K. N. 1969. Cytogenetical studies on some lines of irradiated barley. Unpublished Ph.D. thesis, Banaras Hindu University.
Joachin, G. S. 1947. The product method of calculating linkage from F2 data involving semisterility; and its application to a barley translocation. Genetics 32:580-591.
Prasad, G. and K. Das. 1976. Genetic analysis of four interchanges in barley. Indian J. Genet. 36:102-107.
Robertson, D. W. 1971. Recent information of linkage and chromosome mapping. Barley Genetics 2:220-242.
