The first major step of gene expression and genetic splicing of exons occurs in this specific aqueous environment of the cell.

Nucleus

Explanation:

Expressing a gene basically means manufacturing its corresponding protein. This process has two major steps:

In the transcription process, the information in DNA is transferred to a messenger RNA (mRNA) molecule. This first major step of gene expression and genetic splicing of exons occurs in nucleus environment of the cell.During translation, which is the second major step, the mRNA is "read" according to the genetic code, which relates the DNA sequence to the amino acid sequence in proteins. Within all cells, the translation occurs within a specialized compartment called the ribosome.