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.  

b tumor cells have a cell wall instead of a membrane

explanation:

tumor cells different from normal cells because tumor cells have a cell wall instead of a membrane.