Gaussian mutation. Returns a chromosome where each gene is independently modified with probability mutation_per_gene_rate (default 1.0): a modified gene g in bounds {lo, hi} is replaced by g + sigma * (hi - lo) * N(0, 1) with sigma = gaussian_sigma (default 0.1), clamped to [lo, hi]. Unmodified genes pass through unchanged.

Uniform mutation. Replaces each gene with uniform random in [lo, hi] with probability mutation_per_gene_rate (default 1 / length).