Complex sentence: A white stag or white deer is a red deer with a condition known as leucism, a rare genetic pattern that causes a reduction in the pigment in the animal's hair and skin.
Split into simpler sentences: A white stag or white deer is a red deer with a condition known as leucism that causes its hair and skin to lose its natural colour. Leucism is a rare genetic pattern that causes a reduction in the pigment of an animal's hair and skin.