A woman who is heterozygous for glucose-6-phosphate dehydrogenase (G6PD), a polymorphic enzyme transcribed from the X chromosome, develops chronic myeloid leukemia. Restriction fragment length polymorphism (RFLP) studies on the tumor cells for G6PD reveal that only a single form of the enzyme is transcribed. This finding suppos which of the following features of neoplasia?

**Core Concept**
The question tests the understanding of the concept of neoplastic transformation and its effect on gene expression, specifically in the context of glucose-6-phosphate dehydrogenase (G6PD) enzyme, which is polymorphic and located on the X chromosome.

**Why the Correct Answer is Right**
In normal cells, G6PD exists in two forms due to X-chromosome inactivation, known as Lyonization. However, in neoplastic cells, such as those in chronic myeloid leukemia, the inactivation of one X chromosome is lost, leading to the expression of only one form of the enzyme. This is due to the epigenetic changes that occur during neoplastic transformation, such as loss of heterochromatin and changes in DNA methylation patterns.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not directly related to the concept of neoplasia and gene expression.
* **Option B:** This option is incorrect as it does not relate to the specific scenario of G6PD expression in neoplastic cells.
* **Option D:** This option is not relevant to the concept of neoplasia and gene expression.

**Clinical Pearl / High-Yield Fact**
In neoplastic cells, the loss of heterochromatin and changes in DNA methylation patterns can lead to the reactivation of silenced genes, resulting in the expression of only one form of an enzyme, such as G6PD.

**Correct Answer: C. Loss of X-chromosome inactivation.**

✓ Correct Answer: B. Monoclonality