Male & female differentiation of fetus occurs at –

**Core Concept**
The differentiation of male and female fetuses occurs due to the presence or absence of the SRY gene on the Y chromosome, which triggers the development of testes and subsequently, the production of androgens. This process is crucial for the formation of male genitalia and the development of secondary sex characteristics.

**Why the Correct Answer is Right**
The presence of the SRY gene on the Y chromosome initiates the formation of testes in the genital ridges of the embryo. This is followed by the production of anti-Müllerian hormone (AMH) and testosterone, which inhibit the development of the Müllerian ducts and promote the development of the Wolffian ducts, respectively. The testes then produce Müllerian inhibiting substance (MIS), which prevents the development of the uterus, fallopian tubes, and upper part of the vagina. In the absence of the SRY gene, the genital ridges develop into ovaries, and the production of estrogens and progesterone leads to the development of female genitalia.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify the genetic basis of sex differentiation.
* **Option B:** This option is incorrect because it does not mention the role of the SRY gene in triggering testicular development.
* **Option C:** This option is incorrect because it is too broad and does not specifically address the differentiation of male and female fetuses.

**Clinical Pearl / High-Yield Fact**
It is essential to note that sex differentiation is a complex process that involves the coordinated action of multiple genes and hormones. Abnormalities in this process can lead to various disorders of sex development (DSDs), which require a multidisciplinary approach for diagnosis and management.

**Correct Answer: B. 46-48 days after fertilization**