In karyotype notation, "der" stands for "derived chromosome." This term indicates that the chromosome in question is not present in its normal form but instead has been altered or derived from another chromosome, often as a result of structural rearrangements such as translocations, deletions, or duplications.
When discussing a notation like der(9), it signifies that the derived chromosome is associated with the ninth chromosome. This derived chromosome could result from a variety of genetic events, and identifying such chromosomes is crucial in cytogenetics for understanding genetic abnormalities, particularly in cancer and other genetic disorders.
The other options do not accurately represent the meaning of "der" in karyotype notation. "Dynamic mutation" refers to genetic changes that can involve repeating sequences but is not relevant to chromosome notation. "Detailed analysis" is too vague and does not correlate with the concept of derived chromosomes, and "deformed chromosome" lacks the specificity required in genetic terminology; "deformed" is not a standard term used in this context. Thus, the appropriate understanding of "der" directly aligns with "derived chromosome."