How much human genetic variability is there really?

1000-genomes-consortiumJust how much do each of us human beings vary from each other in our total genome sequence?

The number I was taught at some point was that the genomes of any two human beings are likely to be 99.9% identical. So only about 1 out of 1,000 bp would be different. That still amounts to millions of bp differences, but are perhaps most are not functionally significant? How do you feel about that 99.9% figure?

In talking with some people who are more on top of human genetics they have generally indicated that humans are only somewhere between 99.0-99.5% identical in genomic sequences overall. Wikipedia puts this number at 99.5% if you believe encyclopedias.

Last year a team led by Carlos Bustamante reported finding a striking degree of genetic diversity just in Mexico alone.

Variance in human sequences from person to person can include so-called single nucleotide polymorphisms or SNPs as well as copy number variations (CNVs).

The extent of variability is probably a moving target as well at least in part due to another source of diversity: either developmental mutations or somatic mutations in adults. A recent piece in Science found a remarkable number of somatic mutations in apparently normal skin and some were positively selected.

When big projects like the 1,000 Genomes Project (image above) and then the 100,000 Genomes Project wrap up or even working toward having 1 million people’s genomes sequenced, perhaps we can have a much better handle on this question.

So overall having to answer right now today, how much variability do you see the human genome as having? Take our poll.

6 thoughts on “How much human genetic variability is there really?

  1. Great poll!
    Another followup, is it fair to say that essentially every cell in the human body is genetically distinct?

    If we assume one in 10^-7 bases is not transcribed correctly (on the high end of the Kunkel 2004 estimate), and our shortest chromosome (21) is almost 5 x 10 ^7 base pairs long; it seems to be true on the surface…

  2. Such an important thing to know! Thanks for this post! I hope that reading about skin mutations right before summer will not spoil my holidays 😉

    • Thanks, Pat. I teach about skin here at the UC Davis School of Medicine in the Histology course. I read a figure that was pretty scary. Every skin cell on average during a day out in the sun (not sure if this means with no sun screen) in the summer gets 100,000 mutations. That’s per day per cell. Apparently our cells are so good at repairing DNA that almost every one of those gets corrected and then eventually all those cells are shed. The bigger concern is if our stem cells in our skin get mutated. Yes, all “fun” things to think about as we think about our upcoming summer holidays.

  3. Your post got me interested about epigenetic variability too – do you happen to know the epigenetic variability among humans as a percent?

    • Hi Nikta,
      Great question! I do not know the % variability in the human epigenome, but I’d venture to say it is normally far higher than the genetic variation. Epigenetic states are inherently dynamic even in one person and while our cells mostly have identical DNA sequences, different cells even just in one person can have wildly different epigenomes. So this might be a tough question to answer.

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