What is the process that alters genes and allows variation?

Mutation results in new gene types, the new trait made by the gene; makes variation of two humans. Keep in mind, no two humans are the same; all humans have different heights, appearances and genes. The gene is passed down by sexual reproduction for generations; that is until a recessive (rare) gene appears in a child, then it passes on. This is never ending; and can be applied to dominant (most common) genes also.

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