The abundance and scattered distribution of simple-sequence repeats (SSR) in eukaryotic genomes prompted us to explore the use of SSR-based oligonucleotide primers in single primer amplification reactions. In a pilot experiment, 23 primers were used across a panel of evolutionarily diverse eukaryotic genomes, including grapes, lettuce, tomato, pine, maize, salmon, chicken, Holstein cows and humans. The primers were 16-20 bases in length and represented SSRs of di-, tri-, tetra-, and pentanucleotide repeats. The results showed that tetranucleotide repeat primers were most effective in amplifying polymorphic patterns. Of 11 such primers tested, 70% produced polymorphic patterns from the DNA of one or more species. Primers representing a combination of two tetranucleotide repeats, or compound microsatellites, were equally effective. The polymorphisms contained in such fingerprints were able to identify individuals of vertebrate species as well as lines or varieties of plants. Inheritance of the polymorphic bands was studied in a maize recombinant inbred population, DE811 x B73. Thirty-two polymorphic bands, derived from two amplification patterns, were mapped as dominant markers on an existing RFLP map of the same population. The bands were distributed across nine of the ten chromosomes.

A genetic linkage map has been constructed based on restriction fragment length polymorphism DNA markers for Brassica rapa L. using a segregating F2 progeny from a cross between the yellow sarson type 'R500' and the canola-type 'Horizon'. The map contains 360 marker loci detected by 269 genomic clones derived from a PstI library of 'Westar' (Brassica napus L.). The map consists of 10 linkage groups, covering a total of 1876 recombination units. The occurrence of substantial genome rearrangement during the evolution of B. rapa is evident from (i) a large number of homologous duplicate sequences either at genetically adjacent locations or in different linkage groups and (ii) a number of missing sequences in one or the other parental genome, detected as null alleles. Divergence of the parental genotypes is further supported by the frequency of loci with skewed allele segregation ratios. Comparison of molecular and cytogenetic data on genome structure is discussed. The probe set and map are being used to facilitate rapeseed breeding.Key words: Brassica campestris, Brassica rapa, genome structure, linkage map, restriction fragment length polymorphism.

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