What characterizes chromosomal inversion?

Chromosomal inversion is characterized by a specific rearrangement of the chromosome structure where a segment of a chromosome breaks off, flips around, and then reinserts itself back into the chromosome. This inversion alters the nucleotide sequence's order but does not change the overall amount of genetic material. The inverted segment can affect gene expression, which could have various phenotypic outcomes, depending on the genes involved and their regulatory elements.

The other options describe different chromosomal alterations. For instance, deletion involves the loss of chromosome segments, while replication refers to the duplication of a particular segment. The fusion of chromosomes pertains to processes like translocation or Robertsonian fusion, which do not fit the definition of inversion. Therefore, the confirmation that chromosomal segments are reversed and reinserted clearly aligns with what constitutes a chromosomal inversion.