And because these hemoglobin proteins change their shape, the entire red blood cell also changes its shape. It changes its shape from a biconcave shape to a sickle half moon shape. Now, because of the shape, these red blood cells, the sickle red blood cells, can actually aggregate together and they can form clogs, clots inside the veins of our body because it's inside the veins that our red blood cells have unloaded that oxygen. So the sickle cells slow down the blood flow in our veins and they can clog the veins of our body, leading to tissue damage which can be very, very painful. Painful. Now, let's move on to the third type of Autosole recessive disease found in humans known as cystic fibrosis.