Deep down, we're all stripy. As we grow in the womb, the cells forming our skin migrate across our developing body in stripe-like tracks called Blaschko's lines. These trails don't normally show up in humans, but they're the source of stripes in animals such as cats. This cow has streaks of hair-free skin rather than coloured fur, due to a fault in a gene called TSR2 – involved in hair growth in many mammals including humans – located on one of her X chromosomes. Because cows have two X chromosomes compared with males (who have an X and a Y), they randomly switch one off in every cell to compensate for the double dosage. Due to this random X-inactivation in skin cells, some of them will have to rely on the faulty copy of TSR2 as they grow and migrate in a developing calf, creating the hairless stripes.
BPoD stands for Biomedical Picture of the Day. Managed by the MRC London Institute of Medical Sciences the website aims to engage everyone, young and old, in the wonders of biomedicine. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.
BPoD is also available in Catalan at www.bpod.cat with translations by the University of Valencia.