In which type of mutation is the total amount of DNA in a chromosome reduced?

A deletion mutation involves the loss of a segment of DNA from a chromosome, resulting in a reduction in the total amount of DNA present. This can occur when a part of the chromosome is removed or erased, which can lead to various effects depending on the genes that are affected by the loss. Such mutations can have a significant impact on an organism's phenotype, potentially leading to loss of function in genes or altered genetic regulation.

In contrast, insertion mutations involve the addition of DNA, which increases the total amount of DNA in a chromosome. Point mutations are small-scale changes where a single nucleotide is altered, and while they can affect the function of a gene, they do not change the overall length of the DNA. Inversion mutations involve the reversal of a segment of DNA within a chromosome but do not result in a loss of DNA. Therefore, the correct answer is indeed the deletion mutation, as it directly leads to a decrease in the overall amount of DNA in a chromosome.