Get the graph of up-regulated genes.

        :return Graph: Graph of up-regulated genes.

def get_upregulated_genes_network(self) -> Graph:
        """Get the graph of up-regulated genes.

        :return Graph: Graph of up-regulated genes.
        """
        logger.info("In get_upregulated_genes_network()")

        deg_graph = self.graph.copy()  # deep copy graph
        not_diff_expr = self.graph.vs(up_regulated_eq=False)

        # delete genes which are not differentially expressed or have no connections to others
        deg_graph.delete_vertices(not_diff_expr.indices)
        deg_graph.delete_vertices(deg_graph.vs.select(_degree_eq=0))

        return deg_graph