**Core Concept**
Ichthyosis vulgaris is a common genetic disorder characterized by dry, scaly skin. It is a form of ichthyosis, a group of skin conditions that result from mutations in genes involved in skin barrier function. The inheritance pattern of ichthyosis vulgaris is crucial in understanding its transmission and diagnosis.

**Why the Correct Answer is Right**
Ichthyosis vulgaris is inherited in an autosomal dominant pattern, meaning a single copy of the mutated gene is sufficient to cause the condition. This is due to mutations in the filaggrin gene (FLG), which encodes a protein essential for the proper formation of the skin's natural moisture barrier. Individuals with one mutated allele (a copy of the gene) will express the condition, while those with two normal alleles will be unaffected. The dominant inheritance pattern of ichthyosis vulgaris is a result of the gene's haploinsufficiency, where a single functioning allele is insufficient to maintain normal skin barrier function.

**Why Each Wrong Option is Incorrect**
**Option A:** X-linked dominant inheritance is seen in conditions such as vitamin D-resistant rickets and hypophosphatemic rickets, where the mutated gene is located on the X chromosome and only one copy is sufficient to cause the condition. However, ichthyosis vulgaris is not inherited in this manner.
**Option B:** X-linked recessive conditions, such as hemophilia A and B, are typically seen in males who have only one X chromosome and are thus more susceptible to the condition. Females with one normal and one mutated allele are usually carriers. Ichthyosis vulgaris does not follow this inheritance pattern.
**Option D:** Autosomal recessive conditions, such as sickle cell anemia and cystic fibrosis, require two mutated alleles (one from each parent) to express the condition. Individuals with only one mutated allele are typically carriers and do not express the condition. Ichthyosis vulgaris, however, is not inherited in an autosomal recessive manner.

**Clinical Pearl / High-Yield Fact**
It is essential to note that ichthyosis vulgaris is often associated with other skin conditions, such as atopic dermatitis (eczema) and asthma. This is due to the shared genetic predisposition to skin barrier dysfunction and immune system dysregulation. Recognizing this association can aid in the diagnosis and management of these conditions.

**✓ Correct Answer: C. Autosomal dominant. Ichthyosis vulgaris is inherited in an autosomal dominant pattern.**