The wind is the most important cause of surface currents. When strong and sustained winds blow across the sea, friction drags a thin layer of water into motion. The movement of the very topmost layer of the sea pulls on the water just under, which then in turn starts the layer under it moving.
Nucleoside analogs are the mutagenic chemicals that have a structure that is similar to the normal bases of the nucleotide and thus can be incorporated in the DNA during the process of replication, however as it has different base-pairing rules than the normal nucleotide base it can lead to mutations.
An example of a nucleoside analog is acyclovir which an analog of guanosine.
