I would be interested in knowing how often the popular press has used the word "genome" in the past year (I couldn't find this kind of study, but let me know if it exists).  What I could do was look at the scientific literature and see how many times the word "genome" was used in all scientific publications (here's how you can do that). The answer: nearly ONE MILLION TIMES.  Each year for the past six years, the word has been used in over 40,000 publications. The genome is kind of a big deal in science (for comparison, the word DNA has been used 1.3M times) and it's a big deal to you!

We've already talked about what DNA is here, but how does that relate to the genome? The genome is made up of all the DNA in a organism.  Every single cell in your body (except maybe red blood cells, which shove the DNA out of the cell as part of the process of becoming a red blood cell) contains a copy of your entire genome.  Genomes aren't just in humans.  Every living organism from a bacterial cell to a mushroom to a squirrel to your pet fish or dog or cat or bird, all has a genome.

In humans, the genome is made out of 22 pairs of chromosomes and 2 sex chromosome.  The 22 chromosomes are conveniently named chromosome 1, chromosome 2, chromosome 3...etc.  The two different sex chromosome are named X and Y. Men have one copy of X and one copy of Y (XY) and women have two X chromosomes (XX). You can actually isolate all of the chromosomes and view them using a stain in a process called karyotyping.

Chromosomes are made up of DNA.  Each of the chromosomes is a long string of As, Ts, Cs, and Gs twisted and curled up so that the strand gets big and thick enough to see. Here's a way to think about this - imagine the DNA strand is one strand of your hair.  If you take the hair by the ends and twist it between your fingers, it starts to rotate and curl and twist until the strand is much thicker and shorter than the long skinny piece of hair.  That's what DNA does (with a little help from some friends called histones).  Why does DNA do this?  So it fits inside of your cells.  The human genome is more than 3 billion bases (bases are those As, Ts, Cs, and Gs,) and if stretched from end to end would be 6-10 feet in length.  The largest human cell (the female egg) is 120 micrometers in diameter, which is 0.0004 feet.  See now why reducing the size of the DNA is so important?

And because it's always about size, let's talk about the size of the human genome.  Think it's the biggest?  Not by a long shot.  The plant paris japonica has 40 chromosomes and 150 billion bases (that's 50,000 times the size of the human genome, in case we're counting).  And this is only of the genomes that we've looked at.  So moving forward, keep in mind it's not the size of the genome that matters, it's what the genome does with what it has that matters.

** The majority of scientific literature is stored in an online library managed by the National Institutes of Health called Pubmed. You can search for nearly any scientific article based on any keyword or author. So for example, the Pubmed search for the word "genome" is here. You may or may not have access to the full text of the publications that are listed on Pubmed (the debate about scientific publishing and WHY all the publications aren't freely available to everyone is a long and contentious one, but you can check out some of the discussion in a recent special issue of Nature).  However, there is a version of all publications funded by public money called Pubmed Central. Search here and you can read all of the scientific publications that have been made available - including the 542,069 publications that have the word "genome" in them.

Dr. Cathy Seiler is the Program Manager for the tissue biorepository at St. Joseph's Hospital and Barrow Neurological Institute. She has her BA in Biochemistry and Molecular Biology from Boston University and PhD in the Biological Sciences from Cold Spring Harbor Laboratory. Her research and teaching focuses on genetics, cancer, and personalized medicine. Find her on Facebook at www.facebook.com/thingsitellmymom

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