One proposed cause of such length changes is replication slippage, caused by mismatches between DNA strands while being replicated during meiosis. DNA polymerase, the enzyme responsible for reading DNA during replication, can slip while moving along the template strand and continue at the wrong nucleotide. DNA polymerase slippage is more likely to occur when a repetitive sequence (such as CGCGCG) is replicated. Because microsatellites consist of such repetitive sequences, DNA polymerase may make errors at a higher rate in these sequence regions. Several studies have found evidence that slippage is the cause of microsatellite mutations. Typically, slippage in each microsatellite occurs about once per 1,000 generations. Thus, slippage changes in repetitive DNA are three orders of magnitude more common than point mutations in other parts of the genome. Most slippage results in a change of just one repeat unit, and slippage rates vary for different allele lengths and repeat unit sizes, and within different species. If there is a large size difference between individual alleles, then there may be increased instability during recombination at meiosis.