**Core Concept**
The gene responsible for folic acid transport is a specific transporter that plays a crucial role in the absorption and utilization of folic acid in the body. Folic acid is an essential nutrient for various bodily functions, including DNA synthesis and repair. The gene encoding this transporter is a vital component of the body's folate metabolism pathway.

**Why the Correct Answer is Right**
The gene responsible for folic acid transport is the SLC19A1 gene, which encodes the reduced folate carrier (RFC) protein. This protein is a transmembrane transporter that facilitates the uptake of folate and its derivatives into cells. The SLC19A1 gene is located on chromosome 21. The correct functioning of this gene is essential for maintaining adequate folate levels in the body, which is particularly important during periods of rapid cell division, such as pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct chromosome location of the SLC19A1 gene.
**Option B:** This option is incorrect because it is not the correct gene responsible for folic acid transport.
**Option C:** This option is incorrect because it is not the correct chromosome location of the SLC19A1 gene.

**Clinical Pearl / High-Yield Fact**
The SLC19A1 gene is a well-known example of a gene that is involved in the transport of essential nutrients. Defects in this gene can lead to impaired folate transport, which can result in megaloblastic anemia and other related disorders.

**Correct Answer:** D.