Its no accident that off-spring resemble their parents. Deoxyribonucleic acid or DNA, located within each cell nucleus is a special chemical, that determines our genetic inheritance in a very orderly way. Under the microscope DNA looks like a mass of tangled threads which consist of tiny subunits called genes. Genes carry instructions, sometimes called the blueprint of life, for various characters like hair color, height, eye color. Our genes are received from both mother and father, half from each. Genes instruct our bodies to make proteins - which determines the shape and function of each cell. Each gene controls the production of a particular protein. 
Most genome scientists assume that this DNA diversity, called “somatic mutation” or “structural variation,” is bad. Mutations and other genetic changes can alter the function of the cell, usually for the worse. Disorderly DNA is a hallmark of cancers, and genomic variation can cause a suite of brain disorders and malformations. It makes sense: Cells working off garbled information probably don’t function very well.
In the immune system, DNA diversity is without a doubt essential to health — it’s how our bodies recognize infectious invaders even if we’ve never encountered them before. Our immune cells produce hundreds of millions of unique and distinctive receptors, a vast library that can detect and combat just about any possible foreign agent

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