Final answer:
Option (a), Cri du chat syndrome results from the deletion of most of the small arm of chromosome 5 (5p), leading to nervous system abnormalities and distinct physical features.
Step-by-step explanation:
Cri du chat syndrome is a condition that results from a specific structural change in chromosomes. This syndrome is characterized by nervous system abnormalities and identifiable physical features, which occur because of a deletion of a segment on chromosome 5.
Specifically, most of the small arm of chromosome 5, known as 5p, is missing in individuals with this condition. The syndrome is named after the distinctive high-pitched cry of affected infants, which resembles that of a cat. The correct answer to the question "Cri du chat syndrome results when a portion of chromosome 5 is missing. This is caused by which of the following structural changes to chromosomes?" is a) deletion.