May occur because of mistakes made when dna copies itself during cell divisions or because of environmental factors such as ultraviolet radiation from the sun.

The answer is acquired gene mutation.

Gene mutation is of 2 types- hereditary mutation and acquired mutation.

Hereditary mutations are inherited by parents and lasts a lifetime and it is present in each and every cell in the body like sickle cell anemia, cystic fibrosis.

Acquired mutations does not pass onto the next generation and it happens due to ultraviolet radiation exposure or when a DNA copies itself during cell division like melanoma.

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.