**Core Concept:**
Autosomal dominant inheritance is a mode of genetic inheritance where an abnormal gene (locus) on one of the non-sex chromosomes determines the presence of a genetic disorder in an individual and its offspring. The presence of the abnormal gene on either the X or Y chromosome does not count as autosomal dominant inheritance.

**Why the Correct Answer is Right:**
Autosomal dominant inheritance is characterized by the following key points:
1. The abnormal gene (locus) is located on a non-sex chromosome (autosome).
2. The presence of the abnormal gene on one allele (copy) is sufficient for an individual to exhibit the genetic disorder or be a carrier.

**Why Each Wrong Option is Incorrect:**
A. Option A is incorrect because the abnormal gene is present on a sex chromosome (X or Y), which does not fit the definition of autosomal dominant inheritance.
B. Option B is incorrect because the presence of the abnormal gene on two alleles (copies) is necessary for an individual to exhibit the genetic disorder or be a carrier, not just one allele.
C. Option C is incorrect because the abnormal gene can be inherited from one affected parent, not just two affected parents, making it distinct from autosomal dominant inheritance.
D. Option D is incorrect because the presence of the abnormal gene on one allele is sufficient for an individual to exhibit the genetic disorder or be a carrier, not both alleles.

**Clinical Pearl / High-Yield Fact:**
Autosomal dominant disorders are inherited in approximately 20% of all genetic disorders, making it a common mode of inheritance. Understanding this concept helps in predicting the inheritance pattern and preparing for genetic counseling discussions with patients and their families.

**Correct Answer:**
**Autosomal dominant inheritance** refers to the presence of the abnormal gene on one allele (copy) on a non-sex chromosome (autosome), and the individual can exhibit the genetic disorder or be a carrier.