public int countOverlap(GeneSet gs) {
		GeneSet gsSmall = this, gsLarge = gs;
		if (size() > gs.size()) {
			gsSmall = gs;
			gsLarge = this;
		}

		// Iterate on smaller gene set. Count overlap
		int count = 0;
		for (String gene : gsSmall)
			if (gsLarge.hasGene(gene)) count++;

		return count;
	}