This is a genetic mutation caused by the replacement of a single base nucleotide with another nucleotide. this term also includes insertions or deletions of a single base pair.

The correct answer is point mutation.

Explanation:

A substitution or a point mutation refers to a genetic modification where a single nucleotide base is inserted, modified, or deleted from a DNA or RNA sequence. Point mutations exhibit different effects on the downstream protein product.  

A point mutation generally occurs at the time of the replication of DNA. The origination of point mutations may take place due to spontaneous mutations, which occur at the time of the replication of DNA.  

answer: tributaries flow into rivers.

wetland is a biome that develops when the water gets accumulated in a land exhibiting a huge depression. these form either seasonally or permanently. the water in the wetland comes from rivers, lakes, ocean, flood, rain or other sources. the wetlands includes mangroves, marshes and peatland.

tributaries flow into the rivers develops a wetland because such water will get deposited in the depression and will restrict the original flow of tributary water. hence, water with low drainage current combines with the river water.