Here's why:

* Deletion: A deletion occurs when a segment of a chromosome is lost. This can involve a single base pair (a point deletion) or a larger segment of the chromosome.

* Loss of bases: The statement explicitly mentions the loss of one or more bases, which is a defining characteristic of a deletion.

* Chromosomal change: Deletions are classified as chromosomal changes because they alter the structure of a chromosome.

Important Note: While a deletion is the most likely answer based on the provided information, it's important to consider other possibilities:

* Point mutation: This is a change in a single base pair and may involve the loss of a base. However, point mutations are typically referred to as changes at the DNA level rather than the chromosomal level.

* Inversion: This involves a segment of a chromosome being flipped, which could technically result in the loss of bases at the breakpoints.

However, the statement emphasizes the loss of bases and the chromosomal level of change, making deletion the most fitting description.