Genes are micro-organisms made of DNA (deoxyribonucleic acid); they lie on chromosomes which are in the nucleus (center) of molecules (so you can imagine how small they are!). You can only see them while using an extremely advanced microscope, and even then they are merely vague dots on a rough surface. All organisms have genes, which means all plants, animals and humans you see have something in common with you! Genes determine the characteristics of living things, for example the color and texture of your hair, your skin tone and the shade and shape of your eyes. Genes also influence how living things develop and function. Genes can cause diseases such as depression, diabetes, several types of cancer and many other illnesses.
Genetic diseases are diseases and can be inherited from your biologic parents or other blood relatives. Each year in the United States, 250 thousand babies die of genetic diseases. Some genetic diseases cause death right away, while others merely shorten life by a few years. Genes themselves do not cause the diseases, they depend on the thousands of proteins that create them to do their work properly. When a protein damaged, it becomes mutated, and starts to damage the other proteins. Everyone has genes of diseases inside them (for example the cystic fibrosis gene), yet only some peoples genes are mutated, causing them to have the disease. A "sporadic case" is when a genetic disease appears for the first time in a family. The power of a mutated gene is greater than one of a healthy gene, meaning that a mutated gene can easily overtake a healthy gene and pass the disease around, causing the disease to become more serious. Genetic diseases are a big aspect of the role genes play in life; they also show the negative side of genes, because instead of only one life being spoiled by sickness, two or three can suffer.
Links
What are Genes? + Genetic Diseases