Final answer:
Chromosomal alteration is the term used to describe the alteration in DNA structure without a change in DNA sequence. It occurs when a section of a chromosome breaks off and rejoins incorrectly or does not rejoin at all, leading to serious consequences.
Step-by-step explanation:
The alteration in DNA structure without a change in DNA sequence, such as loose vs. compact DNA, is called chromosomal alteration. Chromosomal alterations are mutations that change the structure of a chromosome. They can occur when a section of a chromosome breaks off and rejoins incorrectly or does not rejoin at all. This can lead to serious consequences, such as developmental delays and abnormalities, as seen in Down Syndrome.