**Question:** Complete failure of fusion of the Mullerian duct leads to:

**Core Concept:** The Mullerian ducts are embryonic structures that develop into the female reproductive system, including the uterus, fallopian tubes, and upper part of the vagina. During fetal development, the Mullerian ducts undergo a process called regression, where the tubal and uterine parts fuse to form the uterus and fallopian tubes, and the vaginal part remains separate.

**Why the Correct Answer is Right:** In the absence of complete fusion, the structures derived from the Mullerian ducts remain separate, leading to a condition known as **Müllerian duct abnormalities**. This can manifest as:

1. Hypospadias: A congenital disorder characterized by the opening of the urethra located at a site on the penis other than the tip. In this case, the urethral opening remains on the ventral surface of the penis instead of its normal location at the tip.
2. Absence of uterus and vagina: The correct answer (D) represents a scenario where the fusion of the Mullerian ducts fails, resulting in the absence of the uterus and vagina. As a result, a woman would not be able to bear a child and may experience menstrual abnormalities or infertility.

**Why Each Wrong Option is Incorrect:**

A. **Hypospadias (Option A):** While hypospadias is indeed a condition associated with incomplete Mullerian duct development, it does not represent the absence of the uterus and vagina.
B. **Absence of vagina only (Option B):** This option does not address the complete absence of the uterus as well, which is essential in the context of female reproductive function.
C. **Absence of uterus only (Option C):** Similar to option B, this option does not account for the complete absence of the uterus and vagina, leading to reproductive issues in women.

**Clinical Pearl:** Understanding Mullerian duct abnormalities is crucial for understanding female reproductive system development and potential clinical implications. Failure of fusion of the Mullerian ducts can lead to severe reproductive issues in women, such as infertility and menstrual abnormalities.

**Correct Answer:** **D.** Absence of uterus and vagina due to incomplete development of Mullerian ducts.