**Question:** Adult polycystic kidney is inherited as

A. Autosomal dominant
B. Autosomal recessive
C. X-linked dominant
D. X-linked recessive

**Correct Answer:** A. Autosomal dominant

**Core Concept:**
Adult Polycystic Kidney Disease (APKD) is a group of genetic disorders characterized by the formation of fluid-filled cysts in the kidneys, leading to impaired kidney function. These disorders can be inherited through different modes of inheritance.

**Why the Correct Answer is Right:**
Adult Polycystic Kidney Disease (APKD) is inherited as Autosomal Dominant (A) because it follows the pattern of inheritance in which one copy of the mutated gene from either parent is sufficient to cause the disease in an offspring. This type of inheritance is characterized by the presence of the normal and abnormal gene on the same chromosome. In this case, the normal gene is responsible for kidney development, while the mutated gene causes cyst formation.

**Why Each Wrong Option is Incorrect:**

A. Autosomal Recessive (C): In this mode of inheritance, both copies of the mutated gene (one from each parent) are necessary for the disease to manifest. This explanation is incorrect for APKD.
B. X-linked Dominant (D): X-linked dominant inheritance is characterized by the presence of the mutated gene on the X chromosome. APKD is not associated with the X chromosome.
C. X-linked Recessive (B): Similar to X-linked dominant, both copies of the mutated gene are essential for the disease to occur. This explanation is incorrect for APKD.

**Clinical Pearl:**
Understanding the mode of inheritance is crucial for genetic counseling and predicting the risk of disease in offspring. In Autosomal Dominant disorders like APKD, the risk of inheriting the disease increases with each child born to an affected parent. In this case, the disease can be present in both male and female offspring. Awareness of these modes of inheritance helps healthcare providers inform patients and their families about the risk of disease transmission in their offspring.