Which of the following is a type of chromosomal structural change known as duplication?

The correct answer identifies duplication as the addition of an extra copy of a chromosome segment. In genetics, duplication refers explicitly to a situation in which a portion of the chromosome is replicated, leading to an increase in the number of copies of that segment. This can result in a variety of genetic outcomes, depending on the function of the genes involved and their interactions with other genetic elements.

The presence of two identical chromosomes in a pair refers to homologous chromosomes, which is a normal state in diploid organisms and does not denote a structural change. Deletion involves the loss of a chromosome segment, which is a different type of structural alteration that can lead to loss of genetic information. The rearrangement of genetic material typically describes processes such as translocation or inversion, which do not specifically imply a duplication. Thus, the defining characteristic of duplication is the presence of an extra copy of a chromosome segment, making it the correct choice.