Three-point linkage data for inr1 g1 r1 on 10L
--Stinard, PS

We report here the results of linkage tests for the locus inr1, which we had previously shown to be on 10L (MNL 71:84). In our previous report, the Inr1 allele was known as da1 since it was recovered from the Coop's da1 stocks. However, since da1 was originally reported to be on chromosome 9 (Emerson, Beadle, and Fraser, Cornell Univ Agric Exp Stn Mem 180, 1935), and was reported to behave in a recessive manner (Eyster, WH, J Hered 22:225, 1931), and since the locus that we are working with is on 10L and acts as a dominant inhibitor of certain R1 alleles (manuscript in preparation), we have named the locus inhibitor of R1 (inr1), and the dominant inhibitor allele Inr1. Whether Inr1 is identical to da1 may never be known for certain. We are continuing to try to recover the recessive dilute aleurone mutant that was described by Eyster, from the Coop's da1 stocks.

The results of a three-point linkage test for inr1, g1, and r1 on chromosome 10 are presented in Table 1. The linkage test was set up as a series of modified backcrosses as indicated in Table 1. The kernels from the first cross (inr1 g1 R1-g / Inr1 G1 R1-S) were all purple since R1-g is not inhibited by Inr1. Kernels from the second cross [(inr1 g1 R1-g / Inr1 G1 R1-S) X inr1 g1 r1-g] segregated for full purple kernels and pale kernels in an approximate ratio of 6:4. Full purple kernels from this cross were grown in our summer nursery, scored for g1, and crossed as males onto an Inr1 G1 R1-S tester in order to evaluate which alleles were present at the R1 locus, and were crossed as females by inr1 G1 R1-S to evaluate whether Inr1 was present. Pale purple kernels were grown, scored for g1, and crossed as females by inr1 G1 R1-S to confirm that Inr1 was present.

The following linkage relationship was established: inr1 - 12.1 - g1 - 12.1 - r1. These data are consistent with the g1 - r1 distance (14 cM) given on the most recent genetic map of chromosome 10. These data place inr1 about 12 centimorgans proximal to g1 on the long arm of chromosome 10.

Table 1. Three-point linkage data for inr1 - g1 - r1.

Definitions: Inr1 = dominant inhibitor of R1 allele.
inr1 = non-inhibitor allele.
R1-S = R1 allele susceptible to inhibition by Inr1 (e. g. R1-d::Catspaw).
R1-g = normal R1-g allele, not susceptible to inhibition by Inr1.
r1-g = recessive colorless aleurone r1-g allele. Is colorless regardless of the allele
at the inr1 locus.

Testcrosses: [(inr1 g1 R1-g / Inr1 G1 R1-S) X inr1 g1 r1-g] X inr1 G1 R1-S and Inr1 G1 R1-S X [(inr1 g1 R1-g / Inr1 G1 R1-S) X inr1 g1 r1-g].
Reg. Genotype No. Totals
0 Inr1 G1 R1-S 43  
  inr1 g1 R1-g 39 82
1 Inr1 g1 R1-g 7  
  inr1 G1 R1-S 5 12
2 Inr1 G1 R1-g 8  
  inr1 g1 R1-S 4 12
1+2 Inr1 g1 R1-S 0  
  inr1 G1 R1-g 1 1
% recombination inr1--g1 = 12.1 +/- 3.2
% recombination g1--r1 = 12.1 +/- 3.2
% recombination inr1--r1 = 24.3 +/- 4.1

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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