Mononucleotide repeats represent an important source of polymorphic microsatellite markers in Aspergillus nidulans

In fungi, microsatellites occur less frequently throughout the genome and tend to be less polymorphic compared with other organisms. Most studies that develop microsatellites for fungi focus on dinucleotide and trinucleotide repeats, and thus mononucleotide repeats, which are much more abundant in fungal genomes, may represent an overlooked resource. This study examined the relative probabilities of polymorphism in mononucleotide, dinucleotide and trinucleotide repeats in Aspergillus nidulans. As previously found, the probability of polymorphism increased with increasing number of repeating units. Dinucleotide and trinucleotide repeats had higher probabilities of polymorphism than mononucleotide repeats, but this was offset by the presence of numerous long mononucleotide repeats within the genome. Mononucleotide microsatellites with 20 or more repeating units have a probability of polymorphism similar to dinucleotide and trinucleotide microsatellites, and therefore, consideration of mononucleotide repeats will substantially increase the number of potential markers available.