Final answer:
The diversity in proteomes among different cell types, despite having the same genome, is due to the dynamic nature of the proteome where different genes are expressed in different cell types, and is studied under the field of proteomics.
Step-by-step explanation:
The observation that liver cells, mammary cells, and skin cells all contain the same genome but have different proteomes can be best explained by the phenomenon that the genome is constant, but the proteome is dynamic; different tissues have the same genes but express different genes. This results in varied proteomes complementing genomics. The study of this is called proteomics. While all cells of a multicellular organism share the same genetic blueprint, the diversity in cellular functions arises because different genes are switched on or off in different cell types. This gene expression is regulated through mechanisms such as alternative splicing of RNA, post-translational modifications of proteins, and protein-protein interactions. This selective expression leads to each cell type producing a unique set of proteins that define its specific functions.