I want to quantify how similar / different tissue specific expression of marker genes is between different age. I plan to do this by quantifying the similarity of their corresponding marker gene dotplots from scRNAseq data.

I have generated the dotplots. The plots are in the format of tissue x marker genes, with expression level and percentage expression for each pair of tissue and marker gene. Tissue and marker genes are exactly the same across dotplots from samples of different age.

I would appreciate pointers on how to do this in R.