**Core Concept**
The deletion of all four alpha globin genes leads to a significant reduction in alpha-globin chains, resulting in a severe form of alpha-thalassemia. This condition is characterized by the absence of alpha-globin chains, which are essential for the production of hemoglobin A.

**Why the Correct Answer is Right**
The deletion of all four alpha globin genes (two on each chromosome 16) results in the production of only beta-globin chains, leading to the accumulation of excess beta-globin chains. This excess results in the formation of tetramers of beta-globin, which precipitate out of the red blood cells and lead to the destruction of red blood cells, resulting in severe anemia. The condition is known as Hb Bart's hydrops fetalis syndrome.

**Why Each Wrong Option is Incorrect**
* **Option A:** Deletion of three alpha globin genes would result in a less severe form of alpha-thalassemia, known as alpha-thalassemia trait (also known as alpha-thalassemia minor).
* **Option B:** Deletion of two alpha globin genes would result in a milder form of alpha-thalassemia, known as alpha-thalassemia trait (also known as alpha-thalassemia minor).
* **Option D:** Deletion of a single alpha globin gene would not result in a significant reduction in alpha-globin chains and would not lead to the severe form of alpha-thalassemia.

**Clinical Pearl / High-Yield Fact**
The severity of alpha-thalassemia is directly related to the number of alpha-globin genes deleted. Remember that the deletion of all four alpha globin genes results in the most severe form of alpha-thalassemia, Hb Bart's hydrops fetalis syndrome.

**Correct Answer: C.** Hb Bart's hydrops fetalis syndrome.