What is the cause of discontinuous synthesis of DNA on one of the parental strands of DNA? What happens ro these short stretches of synthesised DNA?

Explanation

Synthesis of DNA always takes place in 5'`to`3' direction. In a double stranded DNA both strands are anti parallel and complementary. During DNA synthesis as both strands act as templates, only one strand ,i.e.,3'`to`5' can synthesis complementary strand in 5'`to`3' direction.
The other strand, i.e.. 5'`to`3' has to be synthesised in small stretches in opposite direction as replication fork moves to right. That is why DNA synthesis is discontinuous on one of the parental strands of DNA. These small stretches called Okazaki fragments are joined together by DNA ligase enzyme that closes the nicks.