GrainGenes

II. 21 Location of the eceriferum locus cer-zi on barley chromosome 5.

Jens Jensen, Agricultural Department, Risø National Laboratory, DK-4000 Roskilde, Denmark. "R"

Previously, the eceriferum locus cer-e has been located on chromosome 5 by linkage with the loci at and ert-b, and the eceriferum locus cer-zi has been associated with chromosome 5 by translocation studies (Søgaard, 1973). The present report describes a four-point linkage test by which locus cer-zi is located on chromosome 5.

The mutant line with the eceriferum gene cer-zi⁶⁸, kindly provided by Dr. Søgaard, Copenhagen, was crossed with a line homozygous for the genes wst3e, nec1a and B. The segregation for B and cer-zi was scored F2 plants in the field and the segregation for nec1a and wst5 was scored on F3 seedlings in the greenhouse.

Table 1 presents the segregation data as the six possible two-point combinations. It also gives the chi-squares for linkage (X²_L) that have one degree of freedom in all six cases; the recombination percentages (rec.%) with their standard deviations; the crossing-over frequencies in centimorgans (cM) as obtained by the Kosambi mapping function; and chi-squares (X² fit) with their respective degrees of freedom (df) that test the observed segregations against the segregations expected at the recombination estimates. The map shown in Figure 1 gives the linear order and the relative positions of the four loci. It is seen that the distances in centimorgans are approximately additive. The distances between loci nec1, wst5 and B are in agreement with the distances on the current linkage map of chromosome 5 (Jensen, 1977). The cer-zi locus is incorporated in the most recent linkage map (Jensen, 1978). The translocation studies (Søgaard, 1973) suggest that cer-zi is located in the centromere region of chromosome 5. This is in agreement with the present data that place the cer-zi locus to the left of and fairly close to locus nec1, where the centromere is supposed to be (Jensen, 1977). A segregation deviating from the expected 75 per cent for B is indicated by the significant fit in combinations where this locus occurs (Table 1). Such a deviation is, however, known not to affect distance estimates in the type of segregations studied.

Table 1. The F2 segregation and the linkage estimates from the cross cer-zi x B,wst5, nec1.

Figure 1. The linear order of and the distance estimates in cM between the four loci studied.

References:

Jensen, J. 1977.    BGN 7:86-89.

Jensen, J. 1978. Coordinator's report: Chromosome 5, BGN 8:

Søgaard,  A.B. 1973. Continued linkage studies on eceriferum mutants in barley. BGN 3:57-61.

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