**Core Concept**
The ovary determining gene is a crucial genetic factor that influences the development and differentiation of the gonads, specifically in the case of sex determination in humans. This gene plays a vital role in the expression of the female sex phenotype.

**Why the Correct Answer is Right**
The correct answer is **Wnt4**, a gene that encodes a protein involved in the Wnt signaling pathway. Wnt4 is essential for the development of the female reproductive system, including the formation of the ovaries and the expression of female-specific genes. In the absence of Wnt4, the developing gonads will default to a male fate. Wnt4 acts by repressing the expression of male-specific genes, such as Sox9, which is a key regulator of testis development. The Wnt4 gene is therefore critical for the determination of ovarian development and the establishment of the female sex phenotype.

**Why Each Wrong Option is Incorrect**
**Option A:** Not specified - This option does not provide any relevant genetic information related to sex determination or ovarian development.

**Option B:** Not specified - Similar to Option A, this option does not provide any relevant genetic information related to sex determination or ovarian development.

**Option C:** Not specified - This option is also not relevant to the determination of ovarian development or sex determination.

**Clinical Pearl / High-Yield Fact**
Wnt4 is a key regulator of ovarian development, and mutations in the WNT4 gene have been associated with disorders of sex development, including ovotesticular disorder of sex development (OT-DSD). Understanding the role of Wnt4 in ovarian development is essential for the diagnosis and management of patients with sex developmental disorders.

**Correct Answer:** Wnt4