sentences:  Deficient expression of multiple DNA repair genes are often found in cancers, and may contribute to the thousands of mutations usually found in cancers (see Mutation frequencies in cancers).In addition to its role in DNA mismatch repair, MLH1 protein is also involved in meiotic crossing over.MLH1 forms a heterodimer with MLH3 that appears to be necessary for oocytes to progress through metaphase II of meiosis.