An analysis of chromosomes in a culture containing mutated cells may show the loss of one or more bases making up the chromosome this type of chromosomal change is known as

The answer is; deletion mutation

This type of mutation mostly causes a phenomenon called frameshift mutation whereby the 3-codon sequence reading frame is shifted causing the amino acids translated, downstream of the deletion site, to be altered. This can gravely affect the function of the translated proteins and result in genetic disease.