Final answer:
The typical number of chromosomes in a patient's karyotype is 46, which includes 23 pairs. However, in the case of Down Syndrome (Trisomy 21), there are 47 chromosomes due to an extra copy of chromosome 21.
Step-by-step explanation:
The total number of chromosomes in a patient's karyotype is typically 46, which includes 23 pairs. This number can vary if a genetic abnormality is present. In the case of Down Syndrome, which is also known as Trisomy 21, there are 47 chromosomes because there is an extra copy of chromosome 21. Therefore, the correct answer to the number of chromosomes in a patient's karyotype would generally be 46, but in a scenario where a karyotype indicates Down Syndrome, the number would be 47, matching option A.
Referring to the references provided, Down Syndrome is caused by the nondisjunction of chromosome 21. A karyotype displaying Trisomy 21 shows three copies of this chromosome instead of the usual two. The nondisjunction of chromosomes during meiosis can result in an embryo with an extra chromosome 21, leading to this genetic condition.