**Core Concept**
Klinefelter's syndrome is a genetic disorder characterized by the presence of an extra X chromosome in males, leading to various physical and developmental abnormalities. This condition occurs due to aneuploidy, where the typical male karyotype of 46,XY is altered.

**Why the Correct Answer is Right**
In Klinefelter's syndrome, the karyotype is typically 47,XXY, indicating that the individual has 47 chromosomes instead of the usual 46. This extra X chromosome leads to impaired testicular function, hypogonadism, and infertility. The presence of the extra X chromosome also affects the development of secondary sexual characteristics, resulting in tall stature, gynecomastia, and other physical features. The 47,XXY karyotype is the most common pattern seen in Klinefelter's syndrome.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately represent the karyotype associated with Klinefelter's syndrome. A 45,X karyotype is characteristic of Turner syndrome, a different genetic condition.
**Option B:** This option is incorrect because it is a normal female karyotype, not associated with Klinefelter's syndrome. A 46,XX karyotype is typical for females, while a 46,XY karyotype is typical for males.
**Option C:** This option is incorrect because it is a normal male karyotype, not associated with Klinefelter's syndrome. A 46,XY karyotype is typical for males, while a 47,XXY karyotype is characteristic of Klinefelter's syndrome.

**Clinical Pearl / High-Yield Fact**
Klinefelter's syndrome is the most common sex chromosome disorder in males, affecting approximately 1 in every 650 males. Recognizing the characteristic karyotype of 47,XXY is crucial for diagnosing this condition and providing appropriate genetic counseling.

**Correct Answer:** C. 47,XXY