Effects of parental age and polymer composition on short tandem repeat de novo mutation rates.

We have long known that tandem repeats are hypermutable and attributed that hypermutability to slippage during DNA replication. Contradicting this long-held theory, we show that tandem repeats accumulate mutations in maternal germ cells during periods when these cells do not replicate. This bolsters a new consensus that DNA replication is not the only driver of mutagenesis, even at loci where replicative slippage is possible. Patterns shared by certain loci enriched for mutations from older mothers may hint at mechanisms.