Synthesis of an additional DNA in Pachytene and Zygotene
About 0.3% of total DNA complement is synthesized during those 2 stages as a measure of replication repair mechanism.

Reference:

http://www.ncbi.nlm.nih.gov/pubmed/3731943

http://www.nature.com/nature/journal/v219/n5153/abs/219489a0.html