Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: 84pg1
FINE-STRUCTURE PHYSICAL MAPPING OF GENETIC RECOMBINATION SITES
WITHIN A 500 KB CHROMOSOMAL SEGMENT OF THE MAIZE GENOME.
Civardi L 1, PS Schnable 2,3, KJ Edwards 4 and BJ Nikolau 1,
Departments of 1 Biochemistry & Biophysics, 2 Agronomy, and 3
Genetics and Zoology, Iowa State University, Ames, IA 50011; 4
Plant Biotechnology Section, ICI Seeds, Jealotts Hill Research
Station, Bracknell, Berkshire RG11 6EY, UK
There is a growing body of evidence to suggest that maize
genes represent preferred sites for meiotic recombination.
However, little is known regarding the mechanisms of site
selection for recombination sites within the genome. The 0.1 cM
region between the A1 and Sh2 loci on the long arm of chromosome
3 is an ideal subject for meiotic recombination studies because
these two loci confer readily visible kernel phenotypes which
simplifies the isolation of cross-over events. Using published
A1 and Sh2 sequences we have isolated a 500 kb yeast artificial
chromosome (YAC) from a maize YAC library. This YAC includes the
entire physical distance between and including the A1 and Sh2
loci. We have mapped the restriction endonuclease recognition
sites within this YAC and have established that the distance
between A1 and Sh2 is approximately 240 kb. This value agrees
reasonably well with the predicted physical distance based on the
published genetic distance between A1 and Sh2 and size of the
maize genome. Thus, the relationship between the physical and
genetic distances in this region are representative of the maize
genome as a whole. Approaches ased on both intra-genic
recombination and YAC fragmentation vectors (Pavan et al., 1991)
have established that the 5' end of the A1 gene is closest to
Sh2. Using the restriction endonuclease recognition sites as
reference points we are investigating the distribution of single
copy and repetitive DNA sequences, and the distribution of
expressed genes in this 500 kb region. These physical landmarks
will ultimately be correlated with the distribution of meiotic
recombination sites from a collection of several hundred
recombinants that we have generated between A1 and Sh2.
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