The correct answer to this question is deletion. This type of chromosomal alteration has the most drastic consequences. When chromosomes are altered, it causes what is known as a structural abnormality. Although translocation also has its consequences, it will only cause a pair of chromosomes to attach to another piece of chromosome.
However, deletion occurs when a section of the chromosome breaks, followed by a loss of the genetic information inside it. When this happens, it can lead to what is known as chromosomal deletion syndromes. This causes serious physical disability and congenital anomalies.
Although a deletion always comes with severe conditions, the severity of each condition also depends on whether it involves larger deletions or smaller deletions. Aside from the listed effects of chromosomal deletion syndromes, it can also cause birth defects, and these defects can lead to the death of the affected children, especially during childhood.