Simple sequences, which are stretches of DNA consisting of one or a few tandemly repeated nucleotides, are widespread repetitive elements in eukaryotic genomes. These sequences, such as poly(dA).poly(dT) or poly(dG-dT).poly(dC-dA), have been found to be interspersed in many eukaryotic genomes. A systematic survey revealed that most, if not all, types of simple sequences are present in eukaryotic genomes. The authors propose that these sequences arise through common mechanisms like slippage replication and unequal crossover and may not have a general function in gene expression. Evidence supporting this comes from the observation that simple sequences are found in the metabolically inactive micronucleus of the protozoan Stylonychia but not in the active macronucleus. The study also highlights that simple sequences can be clustered in small DNA regions and may serve as recombination hotspots. The research involved hybridizing synthetic simple sequence DNA to genome blots of various organisms, showing that these sequences are present in human, Drosophila, sea urchin, Stylonychia, and yeast genomes. The findings suggest that simple sequences are not essential for normal gene expression and may arise due to random genetic processes rather than functional necessity.Simple sequences, which are stretches of DNA consisting of one or a few tandemly repeated nucleotides, are widespread repetitive elements in eukaryotic genomes. These sequences, such as poly(dA).poly(dT) or poly(dG-dT).poly(dC-dA), have been found to be interspersed in many eukaryotic genomes. A systematic survey revealed that most, if not all, types of simple sequences are present in eukaryotic genomes. The authors propose that these sequences arise through common mechanisms like slippage replication and unequal crossover and may not have a general function in gene expression. Evidence supporting this comes from the observation that simple sequences are found in the metabolically inactive micronucleus of the protozoan Stylonychia but not in the active macronucleus. The study also highlights that simple sequences can be clustered in small DNA regions and may serve as recombination hotspots. The research involved hybridizing synthetic simple sequence DNA to genome blots of various organisms, showing that these sequences are present in human, Drosophila, sea urchin, Stylonychia, and yeast genomes. The findings suggest that simple sequences are not essential for normal gene expression and may arise due to random genetic processes rather than functional necessity.