What must be included when recording the modal number?

When recording the modal number, the inclusion of a marker chromosome is essential because the modal number represents the most common chromosome count in a given cell population. Marker chromosomes are chromosomes that are not easily identifiable and may represent structural abnormalities. They can influence the modal number if they are found in multiple cells within the sample being analyzed.

The modal number gives insight into the overall chromosome composition for the sample, reflecting not only the standard diploid count but also any additional chromosomal variations present, such as marker chromosomes. Understanding this is critical for accurate cytogenetic analysis, especially in the context of genetic disorders or cancer, where the presence of these abnormal chromosomes can be relevant for diagnosis and prognosis.

Other options do not capture the necessary details for properly defining the modal number. Simply listing diploid chromosomes excludes important variations, while ignoring centromere presence does not reflect the actual composition of the chromosomes. Limiting the record to only mutated chromosomes would overlook the full chromosomal context critical for a comprehensive assessment.