Your one genome comes from two. You get 23 chromosomes from Mom (half her genome) and 23 from Dad (half of his). With mitochondrial DNA from your mother, they combine in a new way to make your one-of-a-kind genome. But we can “carry” more than one genome — making us a mosaic of slightly different genomes. Some examples:
Biome. All organisms have a genome, even simple, single-cell creatures like bacteria. You have a microbiome made of trillions of bacteria living on your skin, in your mouth, gut, and intestines. Each one has a genome.
Baby genome. Genetic tests can identify and analyze a baby’s genome while the baby is still inside Mother’s womb. So Mom carries, temporarily, two genomes.
Complex patterns in our genomes. Your body is made up of cells that make a variety of tissues. The DNA in every tissue has mutations that modify the genetic sequence. Even though most mutations are harmless, many cells in our tissues carry pre-cancer mutations. Alterations to the sequence of ATs and CGs are in a wide variety of tissues. A recent study of 29 different tissues revealed the extent of the complex patterns in our genomes:
“Some of the earliest pre-cancerous changes can accumulate more mutations, and eventually, a small proportion of these may become cancer. Tissue mosaics arise as cells accumulate mutations — from DNA errors that creep in during cell division, or because of exposure to environmental factors such as ultraviolet light or cigarette smoke.”
Now that scientists are identifying mosaicism and detecting the early stages of cancer, advanced technology presents a problem. They also need to determine which cells will develop tumors and which will stay healthy. One researcher, Dr. Tomasetti at Johns Hopkins Medicine, says, “ the messy situation is the new normal. The challenge is to figure out up to what point we call something normal.”
Read more about the study in the open-access article in Nature Research Journal titled, “The human body is a mosaic of different genomes.”