Developing microsatellites when they are rare: Trinucleotide repeat loci in the northern mockingbird Mimus polyglottos

The great value of microsatellite loci to population studies spurs their development. However, finding loci is difficult when microsatellites are uncommon in the genome. Because trinucleotide-repeat loci are rare in northern mockingbirds Mimus polyglottos, we sought a new method for developing a suite of loci. Here we show that a bacteriophage cloning vector, Lambda Zap Express (Stratagene, La Jolla, CA, USA) has several features which make it suitable for this purpose. Using this vector, we made a library of 150 000 size-selected clones and screened with an AAT(10) probe; 97 positives were identified. From these, 12 pairs of PCR primers were developed, nine of which amplify polymorphic loci. Certain combinations of these primer pairs enable simultaneous amplification of up to three loci.