During in vivo DNA replication, a is synthesized by RNA primase and provides a free 3' -OH group for DNA polymerase to attach to and, subsequently, add new nucleotides to the template (parent) DNA strand.

Explanation:

1. During DNA replication, RNA primer is required for the initiation of replication, because RNA primer provides a free 3'-OH group for DNA polymerase  to initiate DNA synthesis.

2. RNA primer is synthesize by RNA  primase enzyme.

3. Leading strand of DNA require only one primer at the time of initiation of replication, while lagging strand required many RNA primers at each okazaki fragments.

format change of dna.