Which of the following results from a G-band karyotype is recognized as indicative of a chromosomal abnormality?

The result denoted as 47,XX,+21 is recognized as indicative of a chromosomal abnormality because it reflects the presence of an extra chromosome 21, which is characteristic of Down syndrome (Trisomy 21). In karyotyping, the notation indicates that the individual has 47 chromosomes in total instead of the normal 46, leading to phenotypic and developmental features associated with the condition.

The additional chromosome 21 presents in this configuration suggests an error during meiosis where nondisjunction occurs, causing the gamete to retain an extra chromosome after fertilization. This result is significant in genetic counseling and diagnosis, as it helps identify individuals at risk for specific health issues related to Down syndrome.

In contrast, the other choices depict normal or unremarkable findings: the results showing “No abnormalities detected” and “46,XX” indicate a typical chromosomal complement without alterations. The result “45,X” refers to Turner syndrome, also a chromosomal anomaly, but 47,XX,+21 is much more commonly recognized in clinical settings as a specific condition associated with a well-defined syndrome.