**Core Concept**
Chromosomal mapping is a technique used to identify the location of genes or genetic disorders on a chromosome. It involves analyzing the physical and genetic characteristics of a chromosome to determine the position of a specific gene or mutation.

**Why the Correct Answer is Right**
The correct answer involves a genetic disorder where the mutation affects a specific gene, leading to a characteristic set of symptoms. The chromosomal mapping in this case suggests that the gene responsible for the disorder is located on a specific chromosome, which can be used for genetic testing and counseling. The genetic disorder is caused by a mutation in the gene that codes for a protein involved in a critical cellular process.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not match the chromosomal mapping of the genetic disorder in question. The disorder is not associated with this particular chromosome or gene.
**Option B:** This option is also incorrect because it is a different genetic disorder with a distinct chromosomal mapping. The symptoms and characteristics of this disorder do not match those described.
**Option C:** This option is incorrect because it is a different gene mutation that affects a different protein and cellular process. The chromosomal mapping and symptoms of this disorder do not match those described.

**Clinical Pearl / High-Yield Fact**
When interpreting chromosomal mapping results, it is essential to consider the specific symptoms and characteristics of the genetic disorder, as well as the location of the mutated gene on the chromosome. This information can be used to provide accurate genetic testing and counseling for patients and families affected by the disorder.

**Correct Answer: C. 21**