**Core Concept**
Turner's syndrome is a genetic disorder that occurs in females, characterized by the partial or complete absence of one X chromosome. This results in various physical, developmental, and reproductive abnormalities.

**Why the Correct Answer is Right**
Turner's syndrome is associated with a karyotype of 45,X, where one X chromosome is missing. Infertility is a common feature due to ovarian dysgenesis, which leads to the production of underdeveloped ovaries and streak ovaries. The streak ovary is a characteristic histological feature of Turner's syndrome, where the ovaries are replaced by fibrous tissue. The condition is also associated with cardiovascular abnormalities, such as coarctation of the aorta, which is a narrowing of the aorta.

**Why Each Wrong Option is Incorrect**
**Option A:** Secondary amenorrhea is not a specific feature of Turner's syndrome. Primary amenorrhea is more commonly associated with the condition.
**Option B:** The genotype 46,XX is normal female karyotype; it is not associated with Turner's syndrome.
**Option C:** While infertility is a feature of Turner's syndrome, it is not the most specific or characteristic feature listed in the options.

**Clinical Pearl / High-Yield Fact**
Turner's syndrome is a classic example of a chromosomal abnormality that affects females, highlighting the importance of karyotyping in the diagnosis of reproductive and developmental disorders.

**Correct Answer: D. Streak ovary**