Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: 64pg1
LENGTH POLYMORPHISMS OF SIMPLE SEQUENCE REPEAT DNA AS MOLECULAR
MARKERS IN SOYBEAN.
Perry B. Cregan, Mahinur S. Akkaya, Soybean and Alfalfa Research
Lab, USDA, ARS, Beltsville, MD 20705, and Arvind A. Bhagwat,
Dept. of Agronomy, University of Maryland, College Park, MD
20742.
In the past three years mammalian geneticists have begun to
use a new type of Polymerase Chain Reaction (PCR) generated
genetic marker resulting from variation in the number of repeat
units (n) in Simple Sequence Repeats (SSRs) such as (CA)n,(AAT)n,
and (AGAT)n. One objective of our work was to investigate the
presence and degree of SSR length polymorphism in soybean. Using
PCR primers flanking five soybean SSR loci we found 6, 7, 8, 13,
and 17 product length variants (alleles) a these loci among a
group of 43 soybean genotypes. Because of the high level of
polymorphism of SSR markers in soybean, this type of marker
should be useful in linkage map development as well as to create
unique DNA fingerprints for soybean cultivar identification. In
contrast to the human genome, soybean has few long (CA)n SSRs but
does appear to possess many (AT)n sequences with n exceeding 15.
In order to isolate additional SSR markers we created a library
of 'Williams' soybean DNA and screened for the presence of clones
with (AT)n repeat sequences. Initial sequence data from positive
clones suggest that (AT)n SSRs with n exceeding 15 may occur on
the average of every 300 kbp in the soybean genome. Thus, SSR
length polymorphisms appear to provide an abundant source of
highly polymorphic genetic markers in soybean and perhaps in
other plant species.
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