Slippage synthesis of simple sequence DNA was studied in vitro to understand how these sequences arise in vivo. The study shows that simple sequences can be synthesized from short primers and a polymerase, with the rate depending on sequence-specific slippage but not on fragment length. This suggests that only the ends of the DNA fragments are involved in determining the rate, making slippage a short-range effect. Slippage synthesis occurs on a fixed template, similar to chromosome replication in vivo, indicating that slippage during replication may cause length polymorphism in simple sequences between individuals. Simple sequences are repetitive nucleotide motifs that show length variation between individuals, useful for DNA fingerprinting. This variation is likely due to slippage mutations during DNA replication. The study used various primers and polymerases to investigate slippage synthesis. Results showed that the growth rate of fragments is independent of their length, and that tri-nucleotide repeats grow slower than dinucleotide repeats, suggesting lower slippage rates for tri-nucleotide repeats. The synthesis process involves slippage events creating new overlapping ends, which are then filled by the polymerase. The rate of slippage and the re-establishment of the polymerase-DNA complex determine the growth rate. The study also found that different polymerases affect the synthesis process. T7 polymerase produced uneven growth and smear patterns, while DNA polymerase I and Klenow enzyme produced more consistent results. Slippage synthesis was also observed on a single-stranded template, where the polymerase could slip and create bulges, leading to length variation. These findings suggest that slippage during replication may be the cause of length polymorphism in simple sequences. The study supports the idea that simple sequence synthesis in vitro occurs via slippage reactions, producing unpaired ends that can be filled by a polymerase. The results have implications for understanding in vivo processes, as simple sequences are often flanked by non-repetitive sequences, and their stability may be influenced by repair mechanisms. The mutation rate in simple sequences may be similar in prokaryotes and eukaryotes.Slippage synthesis of simple sequence DNA was studied in vitro to understand how these sequences arise in vivo. The study shows that simple sequences can be synthesized from short primers and a polymerase, with the rate depending on sequence-specific slippage but not on fragment length. This suggests that only the ends of the DNA fragments are involved in determining the rate, making slippage a short-range effect. Slippage synthesis occurs on a fixed template, similar to chromosome replication in vivo, indicating that slippage during replication may cause length polymorphism in simple sequences between individuals. Simple sequences are repetitive nucleotide motifs that show length variation between individuals, useful for DNA fingerprinting. This variation is likely due to slippage mutations during DNA replication. The study used various primers and polymerases to investigate slippage synthesis. Results showed that the growth rate of fragments is independent of their length, and that tri-nucleotide repeats grow slower than dinucleotide repeats, suggesting lower slippage rates for tri-nucleotide repeats. The synthesis process involves slippage events creating new overlapping ends, which are then filled by the polymerase. The rate of slippage and the re-establishment of the polymerase-DNA complex determine the growth rate. The study also found that different polymerases affect the synthesis process. T7 polymerase produced uneven growth and smear patterns, while DNA polymerase I and Klenow enzyme produced more consistent results. Slippage synthesis was also observed on a single-stranded template, where the polymerase could slip and create bulges, leading to length variation. These findings suggest that slippage during replication may be the cause of length polymorphism in simple sequences. The study supports the idea that simple sequence synthesis in vitro occurs via slippage reactions, producing unpaired ends that can be filled by a polymerase. The results have implications for understanding in vivo processes, as simple sequences are often flanked by non-repetitive sequences, and their stability may be influenced by repair mechanisms. The mutation rate in simple sequences may be similar in prokaryotes and eukaryotes.