The development of melanocytes – the cells that give colour to our skin – is a complicated process. Their growth is controlled by a network of many different genes that can switch on and off at different times, as well as triggering others within the network in a cascade of gene activity. By discovering and mapping out the relationships between these genes, scientists hope to reveal how faults in the system can lead to diseases such as melanoma, an aggressive form of skin cancer. Here they’re studying melanocyte development in zebrafish embryos, using colourful dyes to stain particular active genes in cells. Taking ‘snapshots’ at different times of development can gradually build up a picture of the genes responsible for a melanocyte: from stem cell to fully-functioning mature cell.
Newton’s third law says that forces come in equal and opposite pairs. This means that when air exerts lift on an airplane, the airplane also exerts a downward force on the air. This is clear in the image above, which shows a an A380 prototype launched through a wall of smoke. When the model passes, air is pushed downward. The finite size of the wings also generates dramatic wingtip vortices. The high pressure air on the underside of the wings tries to slip around the wingtip to the upper surface, where the local pressure is low. This generates the spiraling vortices, which can be a significant hazard to other nearby aircraft. They are also detrimental to the airplane’s lift because they reduce the downwash of air. Most commercial aircraft today mitigate these effects using winglets which weaken the vortices’ effects. (Image credit: Nat. Geo./BBC2)