The press release for a study being published in the journal Nature essentially says the genetic instructions for making a human being are a jumbled mess that research is just beginning to unravel. The Human Genome Project has a brief overview of what we've learned so far. The surprising finding of this most recent analysis of human DNA how much of the total composition consists of copies.
Genetic variation: Genes usually occur in two copies, one inherited from each parent. Scherer and colleagues found approximately 2,900 genes--more than 10 percent of the genes in the human genome--with variations in the number of copies of specific DNA segments. These differences in copy number can influence gene activity and ultimately an organism's function.
Copy Number Variations Imagine DNA as a book that is being photocopied; the desired outcome is an exact duplicate of the book with all pages arranged in the correct order. If an individual page is accidentally copied two or three or 10 times, there is no change to the text itself, but there is a change in the number of copies of that page. Alternatively, a page might not get copied at all, or a page might be copied once but then get inserted into the wrong chapter. These same mistakes happen in DNA replication as well, with whole segments of DNA being copied a wrong number of times or being copied once but inserted into the wrong location.
The More the Merrier: When genes duplicate, the selective pressure to keep them from mutating may no longer be present. Over time, copies may be rendered nonfunctional, or they may take on a new function. "There are going to be cases where additional copies themselves might have a phenotypic effect, and therefore might confer a selective advantage or disadvantage,"
