**Core Concept**
The process of gene expression differences based on the parent of origin is a fundamental concept in genetics, specifically in the field of epigenetics. This phenomenon is often observed in mammals, particularly in the context of imprinting, where certain genes are expressed based on whether they were inherited from the mother or the father.

**Why the Correct Answer is Right**
The correct answer is related to the concept of parental imprinting, where specific genes are silenced or expressed based on their parental origin. This is often regulated by epigenetic modifications, such as DNA methylation and histone modification, which can be influenced by the parent of origin. For example, the insulin-like growth factor 2 (IGF2) gene is imprinted in mice and humans, meaning it is only expressed from the paternal allele. This is mediated by the presence of a specific DNA methylation pattern on the maternal allele.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specifically relate to the concept of gene expression differences based on parental origin.
**Option B:** This option is incorrect because it refers to a different biological process, specifically the transmission of traits from one generation to the next through non-genetic means.
**Option C:** This option is incorrect because it refers to a specific type of gene expression regulation, rather than the process of gene expression differences based on parental origin.

**Clinical Pearl / High-Yield Fact**
Imprinting disorders, such as Beckwith-Wiedemann syndrome, can result from disruptions in normal imprinting patterns, leading to abnormal gene expression and potentially severe clinical consequences.

**Correct Answer: C. Genomic imprinting.**