Which event will not alter an organism's karyotype?

A sequence inversion involves the reversal of a segment of a chromosome. This rearrangement affects the order of genes, but it does not change the number of chromosomes or the overall structure of the chromosomes within the karyotype. Therefore, the organism's karyotype remains the same in terms of chromosome number and overall appearance.

In contrast, other options directly impact the karyotype. Chromosome duplication creates an extra copy of a chromosome, resulting in a higher chromosome count. Chromosome fusion combines two chromosomes into one, reducing the total chromosome number. Chromosome deletion removes a segment of a chromosome, which can also alter the chromosome count and structure. Each of these changes can affect the overall karyotype, while sequence inversion does not.