title: Intragenic tandem repeats in Daphnia magna: structure, function and distribution.
abstract: BACKGROUND
  Expressed sequence tag (EST) databases provide a valuable source of genetic data in organisms whose genome sequence information is not yet compiled. We used a published EST database for the waterflea Daphnia magna (Crustacea:Cladocera) to isolate variable number of tandem repeat (VNTR) markers for linkage mapping, Quantitative Trait Loci (QTL), and functional studies.
  
  
  RESULTS
  Seventy-four polymorphic markers were isolated and characterised. Analyses of repeat structure, putative gene function and polymorphism indicated that intragenic tandem repeats are not distributed randomly in the mRNA sequences; instead, dinucleotides are more frequent in non-coding regions, whereas trinucleotides (and longer motifs involving multiple-of-three nucleotide repeats) are preferentially situated in coding regions. We also observed differential distribution of repeat motifs across putative genetic functions. This indicates differential selective constraints and possible functional significance of VNTR polymorphism in at least some genes.
  
  
  CONCLUSIONS
  Databases of VNTR markers situated in genes whose putative function can be inferred from homology searches will be a valuable resource for the genetic study of functional variation and selection.
authors.affiliation: Basel University, Zoological Institute, Vesalgasse 1, CH-4051 Basel, Switzerland. i.colson@bangor.ac.uk
authors.forename: Isabelle
authors.initials: I
authors.lastname: Colson
authors.forename: Louis
authors.initials: L
authors.lastname: Du Pasquier
authors.forename: Dieter
authors.initials: D
authors.lastname: Ebert