This may help to answer many questions.  How can we have so many different types of cells and they all carry the same genetic information?  How is it possible for one identical twin to develop cancer while the other does not?  Can we use this control of the gene expression to help cells that may have lost their way?

It is amazing to think that just about all of the cells of the human body has the same DNA.  The full genetic profile with all of the instructions on how to make a human is in almost every cell.  When most students come through the DNA Learning Center, many of them think that there is different DNA inside of these cells.  That red blood cells have different DNA than bone cells and nerve cells.  One way this is done is through the interaction of small methyl groups (-CH₃) that get added to the DNA molecule, which can help to silence a gene that is not needed in some type of cell or at some point of development.  This is a epigenetic “tag” because there is no change to the sequence of DNA, it is just whether or not there is access to the DNA.  The methyl groups that get added make the cell unable to activate that gene.

This addition of methyl groups, called methylation, also can change throughout the course of our life.  So as we get older the interaction of these groups with our DNA can change.  So even with identical twins, who are born with the same DNA, their epigenetic “tags” can vary and occur independent of one another.  And even more, certain lifestyle choices and experiences throughout the life of a person can change the epigenetic profile of an individual.  And then this gets passed on to our children.  So even what a mother eats while pregnant can affect the tags that get passed to their child.  This ultimately will affect the expression of genes in the child.

And now we are using this information to help treat disease, such as cancer.  So if a gene is turned on that shouldn’t be, could we add methyl groups to that section of the DNA to turn it off?  This has started being used as a new therapy for the treatment for certain cancers.

The nucleus, where chromosomal DNA is stored and protected, is not the only source of DNA in a mammalian cell.  Mitochondria have their own 16,569 bp genomes encoding 37 genes involved in the production of biological energy, ATP.  Mutations in these genes have been linked with human diseases including diabetes, cancer, infertility, and neurodegeneration.  Women who carry a mixture of normal and mutated mitochondrial DNA, a condition called heteroplasmy, may be physiologically healthy but risk having seriously ill children.  The birth of Mito and Tracker, at the Oregon Health and Science University (OHSU), suggests that there may be a way for heteroplasmic women to bear healthy, (mostly) biological children.

When one female’s chromosomal DNA is transferred into another’s enucleated egg cell, the first female’s mitochondrial genome is replaced.  The resulting child features mom’s and dad’s chromosomal DNA, but also carries a donor female’s mitochondrial DNA.  Should the DNA transfer technique work in human cells, “who’s my other mommy” could be a question for the courts.