**Core Concept**
Albinism is a group of rare genetic disorders characterized by the inability of the body to produce melanin, a pigment responsible for skin, hair, and eye color. This condition arises due to defects in the enzymes involved in the biosynthesis of melanin from its precursor molecule, tyrosine.

**Why the Correct Answer is Right**
The correct answer is C. Tyrosine, as albinism is caused by mutations in genes encoding enzymes involved in the conversion of tyrosine to melanin. Specifically, the enzyme tyrosinase is crucial for this process, and defects in its gene lead to the development of oculocutaneous albinism type 1 (OCA1). Tyrosinase catalyzes the oxidation of tyrosine to dopa, which is then converted to dopachrome, a precursor to melanin.

**Why Each Wrong Option is Incorrect**
**Option A:** Histidine is an essential amino acid that plays a critical role in various bodily functions, including the synthesis of histamine and glutamate. However, it is not directly involved in melanin production and is therefore not related to albinism.

**Option B:** Cystine is a non-essential amino acid that is formed from the oxidation of two cysteine molecules. While cysteine is an important component of proteins and plays a role in various biochemical processes, it is not directly involved in the biosynthesis of melanin.

**Option D:** Alanine is a non-essential amino acid that serves as a fuel source for the brain and muscles. It is also involved in the metabolism of glucose and the synthesis of pyruvate, but it is not related to melanin production and therefore is not relevant to albinism.

**Clinical Pearl / High-Yield Fact**
Albinism is not just a cosmetic condition; it also increases the risk of skin cancer and vision problems due to the lack of melanin, which provides protection against UV radiation and helps regulate the growth of new blood vessels in the retina.

**✓ Correct Answer: C. Tyrosine**