|MadSci Network: Genetics|
Good question. The answer depends on what you mean by "unique". Humans and other mammals are diploid. That is, each individual carries two copies of each chromosome, one inherited from Mom and one from Dad. Thus, you could say that 50% of a child's DNA is identical to Mom's because it was inherited from Mom. The other 50% of the child's DNA comes from Dad. However, when you look at the sequence of A's T's G's and C's which make up DNA, any two copies of the human genome differ at only one position every thousand base pairs. Thus, the chromosomes inherited from Dad are only different from Mom's at 1 in 1000 bases, or 0.1%. If we average the copy of the genome from Mom (0% different) and the copy from Dad (0.1% different) we can estimate that 0.05% of the kid's genome will differ from Mom. As an aside, where each copy of the human genome is only 0.1% different from any other, the human genome is somewhere between 3 and 5% different from a chimps genome, and approximately 20% different from a mouse's genome. Anyhow, another way to look at "unique" is to say how many new mutations occurred in the copy of the genome inherited from Mom. The error rate in copying the genome from one generation to the next is only about one in a billion base pairs. Because the genome is approximately 3 billion bases long, each child will carry 3 new mutations (on average). Fortunately most of these mutations have no detectable effects. So the copy of the genome inherited from Mom will actually be 0.000001% unique. I hope this helps. Chris firstname.lastname@example.org
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