Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: 96pg1
MAPPING THE SOYBEAN GENOME
Randy Shoemaker 1, Kayla Polzin 1, Andrew Nickell 2 and Eberson
Calvo 3, 1 USDA-ARS-FCR, 2 Department of Agronomy and 3
Department of Zoology and Genetics, Iowa State University, Ames,
IA 50011.
The soybean is considered to be a "diploidized" tetraploid.
We are using our molecular genetic map to characterize the
structure and organization of this very complex genome. About
10-15% of the probes used in the construction of the soybean
molecular genetic map detect 2 or more polymorphic loci.
Occasionally, the linear order of loci on one linkage group
corresponds to the linear order of duplicate loci present on a
second linkage group. This suggests the evolutionary retention
of some relatively large, ancient homeologous segments. Usually,
however, the map position of duplicate loci appears to be random
relative to the linear order of the comparable loci suggesting a
great amount of genome "scrambling". We are reconstructing
molecular maps using 12 independent populations and are mapping
each probe with several restriction enzymes. This approach is
allowing us to identify additional duplicate loci and to further
resolve genome structure. Additionally we have cloned in lambda
EMBL3, 7 of 9 RFLP fragments detected by probing with genomic
clone pA-071, and 3 fragments detected by probing with a cDNA of
sle, a soybean Lea protein. Five loci have been genetically
mapped with pA-071 associated sequences and 3 sle-related loci
also have been genetically mapped. Cross-hybridization among
fragments indicate that the only sequences with detectable
homology between all related fragments is in the immediate
regions detected by pA-071 or the sle probe. Two of the 7
pA-071-related fragments and 2 of the sle-related fragments
appear to be homeologous within a portion of the cloned
fragments, each with a distinct break-point at which homology
ends. We are also currently determining the distribution of
repeated sequences along several of these fragments.
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