Take the gene mutation that causes phenylketonuria, or PKU. People with the disease can't break down the amino acid phenylalanine, a problem that can lead to severe cognitive damage.

Genetic damage to cone cells, which causes colour blindness, is the most common type of gene disorder seen in humans.

Normally zebrafish, which carry the same p53 gene as humans, can survive low doses of radiation, which causes damage to the DNA, because the gene steps in to repair that damage.