Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: 70pg1
WHAT ARE QTL - RELATING QUANTITATIVE AND QUALITATIVE GENETIC
VARIATION IN MAIZE.
M. Lee, L. Veldboom, M. Scanlon, M. James, A. M. Myers, and D. S.
Robertson, IowaState University, Ames, IA 50011.
The genetic and biological basis of mst, if mt all QTL, has
not been determined Robertson and others have proposed that QTL
identified by linkage with molecular markers, and loci identified
through genetic analysis of extreme mutant phenotypes (e.g.,
dwarf mutations) may be attributable to alleles at the same loci.
Observations from maize isozyme and RFLP mapping studies of plant
height suggest that placement of QTL often coincide with
chromosome regions known to contain loci previously defined by
mutant alleles with qualitative effects on height. If the
quantitative effects of QTL and the qualitative effects of the
mutants are indeed attributable to the same loci, mutant
phenotypes induced by transposon insertion may be one of the mst
efficient means of isolating genes contributing to quantitative
genetic variation. Also, QTL mapping studies may provide a very
efficient means of targeting loci not yet identified by an
extreme mutant phenotype. Direct tests of this idea have been
difficult to perform. We have used cDNA clones of known genes
for starch biosynthesis and genomic sequences at, or very closely
linked to transposon-tagged mutants, as RFLP probes for QTL
mapping of kernel weight, plant height and insect resistance.
The genomic sequences include 'Mutator-tagged sites at, or linked
to defective kernel loci (dek), anther ear 1 locus (an1, a
gibberellin-responsive dwarf), public maize probes near the bx1
locus (absence of cyclic hydroxamates which inhibit leaf blade
feeding by European corn borer larvae). The mapping progeny
consisted of 150 F2:3 lines derived from a cross of inbred lines
Mol7 and H99. QTL with significant effects were detected for all
traits. In general, RFLPs identified by dek clones and cDNAs
related to starch biosynthesis were not associated with QTL
for kernel size. However, the an1 probe was within an interval
for a QTL that accounted for nearly 40% of the phenotypic
variation for plant height. Probes near the bxl locus defined
a QTL that accounted for 17% of the phenotypic variation for
resistance to leaf blade feeding by the European corn borer.
Further tests of these associations are in progress.
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