Additional information on Mutator-induced deletions involving the yg2 locus --Donald S. Robertson and Philip S. Stinard Robertson and Stinard (Genetics 115:353-361, 1987) described 12 deletions in the short arm of chromosome nine involving the yg2 locus. Additional deletions of this region, which when homozygous result in the wd phenotype, were described by us in 1988 (MNL 62:24-25). The data from these reports demonstrated that in Mutator stocks, deletions can occur that range in size from small fully male and female transmissible deletions, to larger ones that are fully female transmissible but are not transmitted through the male, to the largest ones that have no male transmission and reduced female transmission.

This last summer, we selected four of the largest deletions reported in our 1987 paper (116-10, 104-7, 117-5, 107-1) to test against sh1, bz1 and wx to determine if any of these loci were within the deleted regions. Plants known to be heterozygous for the deletions were tested. To produce these, plants of the genotype Mu-del/+ were pollinated by yg2 plants. The yellow-green plants from these crosses are deletion heterozygotes. The original Mu-del/+ stock as well as the yg2 male parents carried, but were not homozygous for, sh1, bz1, and wx. The constitution of the c1 alleles was unknown in these stocks. Thus, we could not test for this locus with these deletions. Non-shrunken, starchy kernels with purple aleurone or colorless aleurone from the above crosses were sown and the resulting plants reciprocally crossed with a C1 C1 sh1 sh1 bz1 bz1 wx wx tester stock (Table 1). Because none of the deletions are male transmissible, the predominance of bronze-shrunken kernels when Mu-del/+ stocks are crossed as males indicates that sh1 and bz1 were carried on the non-deleted homologue. The heterozygous deletion parent plants must have been of the genotype Mu-del (C1) Sh1 Bz1 Wx/(C1) sh1 bz1 wx. The occurrence of a few purple kernels in the outcrosses of all these deletion stocks is expected if the proximal ends of the deletions fall short of the bz1 region and if a crossover has occurred between the deletion and the bz1 locus. Thus, the deletions do not involve the bz1 locus. The observation of crossovers in the bz1-wx region confirms this conclusion. Because all the deletions also have crossovers in the c1-sh1 region, the sh1 locus also is not involved in these deletions. The possibility exists, however, that the c1 locus might be involved for three of these deletions (104-7, 117-5, 107-1). The latest map distance for the c1-sh1 region is 3 centiMorgans and between c1 and bz1 is 5 cM. Three of the deletions map within less than 1.5 cM of bz1. On the basis of mapping data alone these three deletions would be expected to have included the sh1 locus. But from the data above it is known that this is not so. Thus, heterozygosity for these deletions must be reducing crossing over in this region. If this is so, it probably is not wise to speculate, on the basis of crossover data alone, whether or not the c1 locus is involved in these deletions. The fourth deletion (116-10) probably falls far short of the c1 locus because of the observed 7% crossing over between the deletion and bz1.

Table 1. Results from crosses of plants of the genotype Mu--del (C or c) Sh Bz Wx/+ (C or c) sh bz wx with C sh bz wx.  (Table unavailable - see hard copy.)

*Pl - purple plump (Sh) kernels, sh-bz = double recessive shrunken bronze. Rare crossovers in the sh-bz region were observed. Kernels were not classified for waxy.

On the basis of previous tests (Genetics 115:353-361, 1987), deletion 116-10 was suggested to be the smallest of the four deletions involved in this report, while 107-1 was thought to be the largest. The crossover data in Table 1 confirm the previous conclusions. The crossover data indicate that the other two deletions are intermediate in size and probably are about the same length.


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