Sex chromosomes are an ideal system to study processes connected with suppressed recombination. We found evidence of microsatellite expansion, on the relatively young Y chromosome of the dioecious plant sorrel (Rumex acetosa, XY1Y2 system), but no such expansion on the more ancient Y chromosomes of liverwort (Marchantia polymorpha) and human. The most expanding motifs were AC and AAC, which also showed periodicity of array length, indicating the importance of beginnings and ends of arrays. Our data indicate that abundance of microsatellites in genomes depends on the inherent expansion potential of specific motifs, which could be related to their stability and ability to adopt unusual DNA conformations. We also found that the abundance of microsatellites is higher in the neighborhood of transposable elements (TEs) suggesting that microsatellites are probably targets for TE insertions. This evidence suggests that microsatellite expansion is an early event shaping the Y chromosome where this process is not opposed by recombination, while accumulation of TEs and chromosome shrinkage predominate later.

• MeSH
• DNA, A-Form genetics   MeSH
• Chromosomes, Plant genetics   MeSH
• Gene Duplication MeSH
• In Situ Hybridization, Fluorescence MeSH
• Humans MeSH
• Chromosomes, Human, Y genetics   MeSH
• Marchantia genetics   MeSH
• Metaphase genetics   MeSH
• Microsatellite Repeats genetics   MeSH
• Models, Genetic MeSH
• Evolution, Molecular * MeSH
• Periodicity MeSH
• Rumex genetics   MeSH
• Base Sequence MeSH
• Sequence Analysis, DNA MeSH
• DNA Transposable Elements genetics   MeSH
• DNA, Z-Form genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA, A-Form MeSH
• DNA Transposable Elements MeSH
• DNA, Z-Form MeSH

We performed PCR of many DNA fragments of 6-32 nucleotides in length. Some of the fragments expanded into kilobase lengths even in the absence of the complementary strand. The dramatic expansion was observed for (CA)8, (TG)8, (CA)4, (CA)6, (CA)12, (TG)4, (TG)6, (TG)12, (TC)10, (GA)10 and other single strands. Similar expansions were exhibited by related trinucleotide repeats (TTG)5, (CAA)5, (TGG)5, and (CCA)5 as well. However even small perturbations of the strict repetitive nature of the DNA primary structure substantially reduced the expansions. The expansion products had properties characteristic for normal Watson-Crick duplexes. Hence either the Taq polymerase and/or other components of the PCR buffer promote homoduplex formation of the nonselfcomplementary fragments, which is necessary to prime the synthesis of the complementary DNA strand, or the Taq polymerase is able to copy the single-stranded DNA template without any priming effect. The present observations have implications for the evolution of genomic DNA, microsatellite length polymorphism as well as the pathological expansions of trinucleotide repeats in the human genome.

• MeSH
• Dinucleotide Repeats genetics   MeSH
• DNA Repeat Expansion genetics   MeSH
• Nucleic Acid Hybridization MeSH
• DNA, Single-Stranded chemistry   genetics   MeSH
• Humans MeSH
• Mutagenesis genetics   MeSH
• Base Pairing MeSH
• Polymerase Chain Reaction * MeSH
• Base Sequence MeSH
• Temperature MeSH
• Trinucleotide Repeats genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA, Single-Stranded MeSH